ra_serf: Fix authz_tests.py #5: "test authz for write operations"
ra_serf: Fix authz_tests.py #5: "test authz for write operations"

"lock a file, target is readonly: should fail" sub-test:

* subversion/libsvn_ra_serf/locks.c
  (lock_info_t): Add reason code to structure
  (handle_lock): Store reason code; create error when we see a 403.
  (svn_ra_serf__lock): Always check error codes.

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