ra_serf: Fix svnsync tests #14: verify that unreadable content is not synced.
ra_serf: Fix svnsync tests #14: verify that unreadable content is not synced.

* subversion/libsvn_ra_serf/update.c
  (handle_stream): If we get a 404, return an error instead of doing nothing.
  (svn_ra_serf__get_file): Give enough info to create error; check for error.

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