Be as specific as possible with error messages about loading authz
configurations in mod_authz_svn.

We were saying AuthzSVNAccessFile even when the AuthzSVNReposRelativeAccessFile
directive had been used.  Now that there is a split groups file, we can't be
sure if it was the AccessFile or the GroupsFile directive that had a problem
if svn_repos_authz_read2() failed.

* subversion/mod_authz_svn/mod_authz_svn.c
  (get_access_conf): If we know the configuration directive that failed
    give it.  If not give a generic description.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1463410 13f79535-47bb-0310-9956-ffa450edef68