## What changes were proposed in this pull request?

`SerializationUtils.clone()` of commons-lang3 (<3.5) has a bug that breaks thread safety, which gets stack sometimes caused by race condition of initializing hash map.
See https://issues.apache.org/jira/browse/LANG-1251.

## How was this patch tested?

Existing tests.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #15548 from ueshin/issues/SPARK-17985.

This reverts commit bfe7885a.

The commit caused build failures on Hadoop 2.2 profile:

```
[error] /scratch/rxin/spark/core/src/main/scala/org/apache/spark/util/Utils.scala:1489: value read is not a member of object org.apache.commons.io.IOUtils
[error]       var numBytes = IOUtils.read(gzInputStream, buf)
[error]                              ^
[error] /scratch/rxin/spark/core/src/main/scala/org/apache/spark/util/Utils.scala:1492: value read is not a member of object org.apache.commons.io.IOUtils
[error]         numBytes = IOUtils.read(gzInputStream, buf)
[error]                            ^
```

## What changes were proposed in this pull request?

`SerializationUtils.clone()` of commons-lang3 (<3.5) has a bug that breaks thread safety, which gets stack sometimes caused by race condition of initializing hash map.
See https://issues.apache.org/jira/browse/LANG-1251.

## How was this patch tested?

Existing tests.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #15525 from ueshin/issues/SPARK-17985.

## What changes were proposed in this pull request?

When documentation is built is should reference examples from the same build. There are times when the docs have links that point to files in the GitHub head which may not be valid on the current release. Changed that in URLs to make them point to the right tag in git using ```SPARK_VERSION_SHORT```

…from its own release version] [Streaming programming guide]

Author: Jagadeesan <as2@us.ibm.com>

Closes #14596 from jagadeesanas2/SPARK-12370.

## What changes were proposed in this pull request?

This PR tries to fix all typos in all markdown files under `docs` module,
and fixes similar typos in other comments, too.

## How was the this patch tested?

manual tests.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11300 from dongjoon-hyun/minor_fix_typos.

This PR added instructions to get flume assembly jar for Python users in the flume integration page like Kafka doc.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #10746 from zsxwing/flume-doc.

- Fixed information around Python API tags in streaming programming guides
- Added missing stuff in python docs

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #8595 from tdas/SPARK-10440.

Author: zsxwing <zsxwing@gmail.com>

Closes #6830 from zsxwing/flume-python and squashes the following commits:

78dfdac [zsxwing] Fix the compile error in the test code
f1bf3c0 [zsxwing] Address TD's comments
0449723 [zsxwing] Add sbt goal streaming-flume-assembly/assembly
e93736b [zsxwing] Fix the test case for determine_modules_to_test
9d5821e [zsxwing] Fix pyspark_core dependencies
f9ee681 [zsxwing] Merge branch 'master' into flume-python
7a55837 [zsxwing] Add streaming_flume_assembly to run-tests.py
b96b0de [zsxwing] Merge branch 'master' into flume-python
ce85e83 [zsxwing] Fix incompatible issues for Python 3
01cbb3d [zsxwing] Add import sys
152364c [zsxwing] Fix the issue that StringIO doesn't work in Python 3
14ba0ff [zsxwing] Add flume-assembly for sbt building
b8d5551 [zsxwing] Merge branch 'master' into flume-python
4762c34 [zsxwing] Fix the doc
0336579 [zsxwing] Refactor Flume unit tests and also add tests for Python API
9f33873 [zsxwing] Add the Python API for Flume

Commons Lang 3 has been added as one of the dependencies of Spark Flume Sink since #5703. This PR updates the doc for it.

Author: zsxwing <zsxwing@gmail.com>

Closes #6829 from zsxwing/flume-sink-dep and squashes the following commits:

f8617f0 [zsxwing] Add common lang3 to the Spark Flume Sink doc

Updates to the documentation are as follows:

- Added information on Kafka Direct API and Kafka Python API
- Added joins to the main streaming guide
- Improved details on the fault-tolerance semantics

Generated docs located here
http://people.apache.org/~tdas/spark-1.3.0-temp-docs/streaming-programming-guide.html#fault-tolerance-semantics

More things to add:
- Configuration for Kafka receive rate
- May be add concurrentJobs

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #4956 from tdas/streaming-guide-update-1.3 and squashes the following commits:

819408c [Tathagata Das] Minor fixes.
debe484 [Tathagata Das] Added DataFrames and MLlib
380cf8d [Tathagata Das] Fix link
04167a6 [Tathagata Das] Merge remote-tracking branch 'apache-github/master' into streaming-guide-update-1.3
0b77486 [Tathagata Das] Updates based on Josh's comments.
86c4c2a [Tathagata Das] Updated streaming guides
82de92a [Tathagata Das] Add Kafka to Python api docs

Author: Patrick Wendell <patrick@databricks.com>

Closes #4638 from pwendell/SPARK-5850 and squashes the following commits:

386126f [Patrick Wendell] SPARK-5850: Remove experimental label for Scala 2.11 and FlumePollingStream.

Important updates to the streaming programming guide
- Make the fault-tolerance properties easier to understand, with information about write ahead logs
- Update the information about deploying the spark streaming app with information about Driver HA
- Update Receiver guide to discuss reliable vs unreliable receivers.

Author: Tathagata Das <tathagata.das1565@gmail.com>
Author: Josh Rosen <joshrosen@databricks.com>
Author: Josh Rosen <rosenville@gmail.com>

Closes #3653 from tdas/streaming-doc-update-1.2 and squashes the following commits:

f53154a [Tathagata Das] Addressed Josh's comments.
ce299e4 [Tathagata Das] Minor update.
ca19078 [Tathagata Das] Minor change
f746951 [Tathagata Das] Mentioned performance problem with WAL
7787209 [Tathagata Das] Merge branch 'streaming-doc-update-1.2' of github.com:tdas/spark into streaming-doc-update-1.2
2184729 [Tathagata Das] Updated Kafka and Flume guides with reliability information.
2f3178c [Tathagata Das] Added more information about writing reliable receivers in the custom receiver guide.
91aa5aa [Tathagata Das] Improved API Docs menu
5707581 [Tathagata Das] Added Pythn API badge
b9c8c24 [Tathagata Das] Merge pull request #26 from JoshRosen/streaming-programming-guide
b8c8382 [Josh Rosen] minor fixes
a4ef126 [Josh Rosen] Restructure parts of the fault-tolerance section to read a bit nicer when skipping over the headings
65f66cd [Josh Rosen] Fix broken link to fault-tolerance semantics section.
f015397 [Josh Rosen] Minor grammar / pluralization fixes.
3019f3a [Josh Rosen] Fix minor Markdown formatting issues
aa8bb87 [Tathagata Das] Small update.
195852c [Tathagata Das] Updated based on Josh's comments, updated receiver reliability and deploying section, and also updated configuration.
17b99fb [Tathagata Das] Merge remote-tracking branch 'apache-github/master' into streaming-doc-update-1.2
a0217c0 [Tathagata Das] Changed Deploying menu layout
67fcffc [Tathagata Das] Added cluster mode + supervise example to submitting application guide.
e45453b [Tathagata Das] Update streaming guide, added deploying section.
192c7a7 [Tathagata Das] Added more info about Python API, and rewrote the checkpointing section.

Updated the main streaming programming guide, and also added source-specific guides for Kafka, Flume, Kinesis.

Author: Tathagata Das <tathagata.das1565@gmail.com>
Author: Jacek Laskowski <jacek@japila.pl>

Closes #2254 from tdas/streaming-doc-fix and squashes the following commits:

e45c6d7 [Jacek Laskowski] More fixes from an old PR
5125316 [Tathagata Das] Fixed links
dc02f26 [Tathagata Das] Refactored streaming kinesis guide and made many other changes.
acbc3e3 [Tathagata Das] Fixed links between streaming guides.
cb7007f [Tathagata Das] Added Streaming + Flume integration guide.
9bd9407 [Tathagata Das] Updated streaming programming guide with additional information from SPARK-2419.