Add more http status verifications in libsvn_ra_serf.

* subversion/libsvn_ra_serf/options.c
  (svn_ra_serf__v2_get_youngest_revnum,
   svn_ra_serf__v1_get_activity_collection,
   svn_ra_serf__exchange_capabilities): Report anything but 200 as unexpected.
  (svn_ra_serf__probe_proxy): Expect either 200 or 411.
  (svn_ra_serf__has_capability): Add error tracing.

* subversion/libsvn_ra_serf/property.c
  (svn_ra_serf__wait_for_props): Expect 207 status.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1553881 13f79535-47bb-0310-9956-ffa450edef68