ra_serf: Fix buglet when we lose a response; better handle the get file case where the file doesn't exist on HEAD.
ra_serf: Fix buglet when we lose a response; better handle the get file case
where the file doesn't exist on HEAD.

* subversion/libsvn_ra_serf/update.c
  (handle_fetch): Set len to be the difference: = not +=.  (grr.)
  (svn_ra_serf__get_file): Implement searching for a missing file because
  peg-revs don't actually come into play here (though they should).

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion