Add ability to CANCEL re-INVITEs

Ignore-this: 2fced2cd90a2caab175ba280bd452060

darcs-hash:20100204144126-56b4d-b8b15c635cc5dbae1d13aa4447c2f3968aac7872
Changed the way NotificationProxyLogger sends MSRP trace notifications

Ignore-this: fd9d347dc9cb6840fc85aed61ed31883

darcs-hash:20100204114743-1e3d8-25f916893e05e399fa80e25c50a1f8a82e9d5c81