Sync'ing FSX with FSFS:
Merge r1510901,-96 from /branches/fsfs-improvements/subversion/libsvn_fs_fs
into /trunk/subversion/libsvn_fs_x.  No conflicts. Docstring fixes only.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1595092 13f79535-47bb-0310-9956-ffa450edef68