Rename Split to Partition, per Spark commit

https://github.com/mesos/spark/commit/06e5e6627f3856b5c6e3e60cbb167044de9ef6d4#core/src/main/scala/spark/Partition.scala
Removed EnhancedRDD and use Spark's PartitionPruningRDD instead.
Changed Spark version to 0.7.0.
SHARK-123: Detect mapred.map.tasks and use it in TableScanOperator.

https://spark-project.atlassian.net/browse/SHARK-123
Merge branch 'amplab'