Fix handling of empty SPARK_EXAMPLES_JAR
SPARK-1005 Ning upgrade
Made java options to be applied during tests so that they become self explanatory.
Add warning to null setJars check
Clarify spark.cores.max

It controls the count of cores across the cluster, not on a per-machine basis.
Change protobuf version for yarn alpha back to 2.4.1
Merge pull request #330 from tgravescs/fix_addjars_null_handling

Fix handling of empty SPARK_EXAMPLES_JAR

Currently if SPARK_EXAMPLES_JAR is left unset you get a null pointer exception when running the examples (atleast on spark on yarn).  The null now gets turned into a string of "null" when its put into the SparkConf so addJar no longer properly ignores it. This fixes that so that it can be left unset.
Merge pull request #342 from tgravescs/fix_maven_protobuf

Change protobuf version for yarn alpha back to 2.4.1

The maven build for yarn-alpha uses the wrong protobuf version and hence the generated assembly jar doesn't work with Hadoop 0.23.  Removing the setting for the yarn-alpha profile since the default protobuf version is 2.4.1 at the top of the pom file.
Merge pull request #341 from ash211/patch-5

Clarify spark.cores.max in docs

It controls the count of cores across the cluster, not on a per-machine basis.
Merge pull request #338 from ScrapCodes/ning-upgrade

SPARK-1005 Ning upgrade
Merge pull request #340 from ScrapCodes/sbt-fixes

Made java options to be applied during tests so that they become self explanatory.
Fix test breaking downstream builds
Merge pull request #343 from pwendell/build-fix

Fix test breaking downstream builds

This wasn't detected in the pull-request-builder because it manually sets SPARK_HOME. I'm going to change that (it should't do this) to make it like the other builds.
Minor typo fix for yarn client
Export --file for YarnClient mode to support sending extra files to worker on yarn cluster