SPARK-1008: Logging improvments

1. Adds a default log4j file that gets loaded if users haven't specified a log4j file.
2. Isolates use of the tools assembly jar. I found this produced SLF4J warnings
   after building with SBT (and I've seen similar warnings on the mailing list).
Response to Shivaram's review
Removing initLogging entirely
Minor fixes
Removing use in test
Tiny typo fix
Adding outer checkout when initializing logging
Merge remote-tracking branch 'apache-github/master' into log4j-fix-2

Conflicts:
	streaming/src/main/scala/org/apache/spark/streaming/scheduler/JobGenerator.scala
Merge pull request #312 from pwendell/log4j-fix-2

SPARK-1008: Logging improvments

1. Adds a default log4j file that gets loaded if users haven't specified a log4j file.
2. Isolates use of the tools assembly jar. I found this produced SLF4J warnings
   after building with SBT (and I've seen similar warnings on the mailing list).
Merge remote-tracking branch 'apache/master' into conf2

Conflicts:
	core/src/main/scala/org/apache/spark/SparkContext.scala
	core/src/main/scala/org/apache/spark/metrics/MetricsSystem.scala
	core/src/main/scala/org/apache/spark/storage/BlockManagerMasterActor.scala
Miscellaneous fixes from code review.

Also replaced SparkConf.getOrElse with just a "get" that takes a default
value, and added getInt, getLong, etc to make code that uses this
simpler later on.