sip_msrp_client.py: prefer to use shutdown over end as the former does not raise

darcs-hash:20081119074426-b2873-8b420d79160fbc2692ab138acc2afec34276131a
_format_reason: do not print 200 OK

darcs-hash:20081119080158-b2873-b9c403089d0b2655ace80d8c78336fdf691cab24