enginebuffer: removed methods _wait and wait_incoming, added methods link,unlink,link_incoming; the former could lose pypjua events

darcs-hash:20090127091135-b2873-6e81e72ad4355e11f6cddda539ebaa0c7489b101
sip_im_session: don't exit if the registration has failed

darcs-hash:20090127091332-b2873-e687abcfb78da225ed6bbae74ec1717322b834f4