Added "local_uri", "remote_uri" and "is_outgoing" convenience attributes to Invitation class

darcs-hash:20090122154352-58103-4aeb1000c9e50769bf280d1dba339355506bb08d
sip_im_session: added --no-register option

darcs-hash:20090123094223-b2873-1a47ea707602261f5ca5458be028ac1f84618dd7