ra_serf: Replace bunch of abort() calls with errors.
ra_serf: Replace bunch of abort() calls with errors.

* subversion/libsvn_ra_serf/update.c
  (start_report): Generate error when mandatory XML attribute not found in
   update-report response.
  (end_report): Generate error on unknown prop encoding instead of abort().

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