use StateLogger of msrplib to log MSRP connection state

darcs-hash:20090121092139-b2873-72dfe81154b740c60517067dc251343d482a5047
Added missing internal boolean to Invitation class to allow set_state_DISCONNECTED to be called more than once, also makes __dealloc__ work correctly

darcs-hash:20090121125930-58103-c75ecadcf070ff6a3680b2b2020962fb32befa0a