Sync'ing FSX with FSFS:
Record changes of /subversion/libsvn_fs_fs up to r1512300 
as already merged into /subversion/libsvn_fs_x. 

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1595098 13f79535-47bb-0310-9956-ffa450edef68