Another round of Netty fixes.
1. Avoid race condition between stop and copier completion
2. Handle socket exceptions by reporting them and filling in a failed
FetchResult
Make connect timeout configurable
Delete a file for a block if it already exists.
Reuse the file object as it is valid after delete
var to val
Don't write zero block files with java serializer
Pass in bufferSize to BufferedOutputStream
Clean up variables and counters in BlockFetcherIterator
Merge branch 'master' of git://github.com/mesos/spark into netty-dbg
Merge branch 'netty-dbg' of github.com:shivaram/spark into netty-dbg
Fix some comments and style
Merge pull request #648 from shivaram/netty-dbg

Shuffle fixes and cleanup