Try to confirm a guess why the redirect tests fail on the centos buildbot.

* subversion/libsvn_ra_serf/util.c
  (response_get_location): Construct full uri, if the location header starts
    with a '/'.
  (handle_response): Update caller.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1443772 13f79535-47bb-0310-9956-ffa450edef68