Paranoid uncaught exception handling for exceptions during shutdown
Catch/log errors deleting temp dirs
Added a method to create PartitionPruningRDD.
Fixes link to issue tracker in documentation page "Contributing to Spark".
Merge pull request #483 from rxin/splitpruningrdd2

Added a method to create PartitionPruningRDD.
Merge pull request #484 from andyk/master

Fixes a broken link in documentation to issue tracker
Pull detection of being in a shutdown hook into utility function.
Merge pull request #482 from woggling/shutdown-exceptions

Don't call System.exit over uncaught exceptions from shutdown hooks