A few more style fixes in `yarn` package.
Add a "new-yarn" directory in SPARK_HOME, intended to contain Hadoop-2.2 API changes.
Hadoop 2.2 YARN API migration for `SPARK_HOME/new-yarn`
Add optional Hadoop 2.2 settings in sbt build.

If the Hadoop used is version 2.2 or derived from it, then Spark
will be compiled against protobuf-2.5 and a protobuf-2.5 version of
Akka 2.0.5.