Include the groups file in the cache_key for mod_authz_svn.

This prevents a potential security issue.  If we neglected to include the
groups file in the cache key and two repos were configured with the same
authz file but not the same groups file then the groups file would be used
for whichever repo was accessed first in a connection.  Potentially,
allowing a user to escalate the privledges they have on a repo.

* subversion/mod_authz_svn/mod_authz_svn.c
  (get_access_conf): Add groups_file to the cache_key string.



git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1463408 13f79535-47bb-0310-9956-ffa450edef68