Sync FSX with FSFS.  Block txn dir cache cleanup changes as FSX does
not use separate cache instances for it anymore:
r1643139 and r1643233.

* subversion/libsvn_fs_x
  (): Update mergeinfo.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1645582 13f79535-47bb-0310-9956-ffa450edef68