Re-added and improved incoming account check in SessionManager

darcs-hash:20090326110626-58103-be87d50812e8adc242c4fb7f5cb17aaea2b499ff
Make other accounts than selected one not register in sip_message.py

darcs-hash:20090326112531-58103-7203a9e93bb94df8765df882d1ce6a8cbb2bdae9