This uses a seperate Hadoop version for YARN artifact. This means when people link against
spark-yarn, things will resolve correctly.

This includes the following changes:
- The "assembly" package now builds in Maven by default, and creates an
  assembly containing both hadoop-client and Spark, unlike the old
  BigTop distribution assembly that skipped hadoop-client
- There is now a bigtop-dist package to build the old BigTop assembly
- The repl-bin package is no longer built by default since the scripts
  don't reply on it; instead it can be enabled with -Prepl-bin
- Py4J is now included in the assembly/lib folder as a local Maven repo,
  so that the Maven package can link to it
- run-example now adds the original Spark classpath as well because the
  Maven examples assembly lists spark-core and such as provided
- The various Maven projects add a spark-yarn dependency correctly

This reverts commit 1fb1b099, reversing
changes made to c69c4894.

It made the JSON creation slightly more complicated, but reduces one external dependency. The scala library also properly escape "/" (which lift-json doesn't).

Also add jblas dependency to mllib pom.xml

This is used to find methods in the Scala API that
need to be ported to the Java API.  To use it:

  ./run spark.tools.JavaAPICompletenessChecker
Conflicts:
	project/SparkBuild.scala
	run
	run2.cmd