JIRA issue: [SPARK-2190](https://issues.apache.org/jira/browse/SPARK-2190)

Added specialized in-memory column type for `Timestamp`. Whitelisted all timestamp related Hive tests except `timestamp_udf`, which is timezone sensitive.

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #1440 from liancheng/timestamp-column-type and squashes the following commits:

e682175 [Cheng Lian] Enabled more timezone sensitive Hive tests.
53a358f [Cheng Lian] Fixed failed test suites
01b592d [Cheng Lian] Fixed SimpleDateFormat thread safety issue
2a59343 [Cheng Lian] Removed timezone sensitive Hive timestamp tests
45dd05d [Cheng Lian] Added Timestamp specific in-memory columnar representation