Added a BlockObjectWriter interface in block manager so ShuffleMapTask
doesn't need to build up an array buffer for each shuffle bucket.
concurrentRestrictions fails for this PR - but works for master, probably some version change
Allow changing the serializer on a per shuffle basis.
Allow the specification of a shuffle serializer in the read path (for
local block reads).
Add an interface to zip iterators of multiple RDDs
The current code supports 2, 3 or 4 arguments but can be extended
to more arguments if required.
Rename to zipPartitions and style changes
Attempt to fix streaming test failures after yarn branch merge
Merge branch 'master' of github.com:mridulm/spark
Allow CheckpointWriter pending tasks to finish
Remove spurious commit
Make log message more descriptive to aid in debugging
Remove debug statements
Merge pull request #583 from mridulm/master

Fix issues with streaming test cases after yarn branch merge
Rename classes from MapZipped* to Zipped*
Actually rename classes to ZippedPartitions*
(the previous commit only renamed the file)
Rename partition class and add scala doc
Merge pull request #582 from shivaram/master

Add zip partitions interface
Fix BlockManagerSuite to deal with clearing spark.hostPort
More unit test fixes
Spark-742: TaskMetrics should not employ per-record timing.

This patch does three things:

1. Makes TimedIterator a trait with two implementations (one a no-op)
2. Makes the default behavior to use the no-op implementation
3. Removes DelegateBlockFetchTracker. This is just cleanup, but it seems like
   the triat doesn't really reduce complexity in any way.

In the future we can add other implementations, e.g. ones which perform sampling.