Note that we use scala.Serializable introduced in Scala 2.9 instead of
java.io.Serializable. Also, case classes inherit from scala.Serializable by
default.
This merge keeps only the broadcast work in mos-bt because the structure
of shuffle has changed with the new RDD design. We still need some kind
of parallel shuffle but that will be added later.
Conflicts:
core/src/main/scala/spark/BitTorrentBroadcast.scala
core/src/main/scala/spark/ChainedBroadcast.scala
core/src/main/scala/spark/RDD.scala
core/src/main/scala/spark/SparkContext.scala
core/src/main/scala/spark/Utils.scala
core/src/main/scala/spark/shuffle/BasicLocalFileShuffle.scala
core/src/main/scala/spark/shuffle/DfsShuffle.scala
