Merged revision(s) 1586407 from lucene/dev/trunk:
LUCENE-5588: Lucene now calls fsync() on the index directory, ensuring that all file metadata is persisted on disk in case of power failure.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1586410 13f79535-47bb-0310-9956-ffa450edef68