In ra serf: Handle all http errors except 404 as failures, instead of just a
few specific ones. This avoids running the xml parser on raw http errors,
which just causes hard to understand errors.

The exception for 404 is currently the only case that code expects to get
through as non error in a few places.

* subversion/libsvn_ra_serf/util.c
  (handle_response): Handle all http errors except code 404 as error.

* subversion/tests/cmdline/authz_tests.py
  (log_diff_dontdothat): Remove XFail and expect a cleaner error.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1552043 13f79535-47bb-0310-9956-ffa450edef68