HDFS-5554. Flatten INodeFile hierarchy: Replace INodeFileWithSnapshot with FileWithSnapshotFeature.  Contributed by jing9


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1548796 13f79535-47bb-0310-9956-ffa450edef68
Merge remote-tracking branch: upstream/trunk