further prune column for TachyonTableRDD
1. rename addColumnPruneInfo to be pushDownColumnPruning. 2. let TablePartition ignore null ByteBuffer in prunediterator.
Spark package rename (spark -> org.apache.spark).
Merge pull request #142 from amplab/tachyon

further prune column for TachyonTableRDD
Try to fix configuration problem for user
Changed spark package in ci script.
Merge pull request #143 from rxin/rename

Spark package rename (spark -> org.apache.spark).
Merge pull request #144 from pwendell/exception

Try to fix configuration problem for user
Updated sbt project setting for assembly target.
Add some misc. comments in TableScanOperator.
Merge branch 'master' of git://github.com/amplab/shark

Conflicts:
	src/main/scala/shark/execution/TableScanOperator.scala
Comments for MemoryMetadataManager::unpersist()
Update some misc comments for TableScanOperator/MetadataManager
Merge pull request #145 from harveyfeng/partition-caching

Some misc. comments in TableScanOperator and MemoryMetaDataManager