CHANGES for HDFS-347 branch.
These will be integrated to trunk CHANGES.txt after merge


HDFS-4353. Encapsulate connections to peers in Peer and PeerServer classes.
(Colin Patrick McCabe via todd)

HDFS-4354. Create DomainSocket and DomainPeer and associated unit tests.
(Colin Patrick McCabe via todd)

HDFS-4356. BlockReaderLocal should use passed file descriptors rather than paths.
(Colin Patrick McCabe via todd)

HDFS-4388. DomainSocket should throw AsynchronousCloseException when appropriate.
(Colin Patrick McCabe via todd)

HDFS-4390. Bypass UNIX domain socket unit tests when they cannot be run.
(Colin Patrick McCabe via todd)

HDFS-4400. DFSInputStream#getBlockReader: last retries should ignore the cache
(Colin Patrick McCabe via todd)

HDFS-4401. Fix bug in DomainSocket path validation
(Colin Patrick McCabe via todd)

HDFS-4402. Some small DomainSocket fixes: avoid findbugs warning, change log level, etc.
(Colin Patrick McCabe via todd)