Fix a bug in the recursive authz lookup algorithm within mod_authz_svn.

This is a backport of r15463 to the 1.2.x branch.

Patch by:     Bernd Rinn <bernd@sdf.lonestar.org>
Review by:  David Anderson <david.anderson@calixo.net>

* subversion/mod_authz_svn/mod_authz_svn.c
  (authz_path_is_ancestor): New internal function.
  (parse_authz_section): Use authz_path_is_ancestor to establish
    relationships between paths instead of just strncmp.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.2.x-authz@855541 13f79535-47bb-0310-9956-ffa450edef68