LUCENE-5730: FSDirectory.open should return mmap for 64-bit OS X

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1599725 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5725: fix changes typo

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1599733 13f79535-47bb-0310-9956-ffa450edef68