Sync'ing FSX with FSFS: 
Record all changes from /branches/fsfs-improvements/subversion/libsvn_fs_fs
as already merged into /trunk/subversion/libsvn_fs_x.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1595093 13f79535-47bb-0310-9956-ffa450edef68