HDFS-5433. When reloading fsimage during checkpointing, we should clear existing snapshottable directories. Contributed by Aaron T. Myers.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1537192 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5432. TestDatanodeJsp fails on Windows due to assumption that loopback address resolves to host name localhost. Contributed by Chris Nauroth.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1537230 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5386. Add feature documentation for datanode caching. Contributed by Colin Patrick McCabe.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1537243 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd