Sync FSX with FSFS:
Record-only merge r1619413 r1619769 and r1632926 from libsvn_fs_fs.

These revprop caching changes have been superseded by the new caching
code merged to FSX in r1632907.

* subversion/libsvn_fs_x
  (): Update mergeinfo.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1634943 13f79535-47bb-0310-9956-ffa450edef68