Allow SVNAuthzGroupsFile to accept repos-relative paths.  Inadvertingly broke
this with r1463374.

* subversion/mod_authz_svn/mod_authz_svn.c
  (resolve_repos_relative_url): Split the logic to resolve a repos-relative
    URL out into a separate function.
  (get_access_conf): Use resolve_repos_relative_url() to resolve repos-relative
    URLs for both the AccessFile and the GroupsFile.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1463401 13f79535-47bb-0310-9956-ffa450edef68