Add a bit more self-checking in fsfsfixer.

* contrib/server-side/fsfsfixer/fixer/fix-rev.py
  (replace_in_file): Detect failure to do the replacement.
  (replace_in_rev_file): Add a doc string.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1441448 13f79535-47bb-0310-9956-ffa450edef68