HDFS-5425. Renaming underconstruction file with snapshots can make NN failure on restart. Contributed by Vinay and Jing Zhao.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1541261 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-YAHOO-202-trunk-gd