Sync'ing FSX with FSFS:
Merge r1549924,1549926,1553045,1553046 from /subversion/libsvn_fs_fs
into subversion/libsvn_fs_x.  Conflicts were due structural differences
between FSX and FSFS.

This ports "the move indexes into place" fixes.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1595578 13f79535-47bb-0310-9956-ffa450edef68