smbd: Support multiple dfs targets for msdfs proxy shares

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Björn Jacke <bj@sernet.de>
doc/msdfs proxy: extend example for multi target config

Signed-off-by: Björn Jacke <bj@sernet.de>
Reviewed-by: Michael Adam <obnox@samba.org>

Autobuild-User(master): Björn Jacke <bj@sernet.de>
Autobuild-Date(master): Fri Nov  1 00:12:19 CET 2013 on sn-devel-104