On the revprop-caching-ng branch:  Guarantee no lost updates on
revprop generation files.

* subversion/libsvn_fs_fs/revprops.c
  (begin_revprop_change): Always close and re-open the file to make
                          sure we don't get stale OS file buffers.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/revprop-caching-ng@1620241 13f79535-47bb-0310-9956-ffa450edef68