AudioStream: make error more helpful to debuggers

darcs-hash:20090422104058-b2873-060302d54bdeb786ec82774ed786b66171913495
sip_session2: fix dtmf

- move a couple of functions from ChatSession to ChatManager where they are more relevant

darcs-hash:20090422104250-b2873-e5106eb9b77780daba0f1acf729d810fef18252d