Sync'ing FSX with FSFS:
Merge r1559912,1560107,1586947,1586953 from /subversion/libsvn_fs_fs
into subversion/libsvn_fs_x.  Conflicts were due to name and structural
differences between FSX and FSFS.

This ports the 'svn log' related changes.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1595344 13f79535-47bb-0310-9956-ffa450edef68