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

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1599732 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5725: fix changes typo

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1599735 13f79535-47bb-0310-9956-ffa450edef68