nta: when in UAS mode, respond to CANCEL and INVITE with same tag
nta: when in UAS mode, respond to CANCEL and INVITE with same tag

Added mreply(), internal function for responding to a request message
Also, tag INVITE before responding to CANCEL.

darcs-hash:20080814152121-db55f-b683aac0f9c715548589730ad4d3c7be6e3177fe.gz

unispeech/sofia-sip,BelledonneCommunications/sofia-sip,unispeech/sofia-sip,unispeech/sofia-sip,jart/sofia-sip,erdincay/sofia-sip,unispeech/sofia-sip,jart/sofia-sip,BelledonneCommunications/sofia-sip,BelledonneCommunications/sofia-sip,xhook/sofia-sip,xhook/sofia-sip,BelledonneCommunications/sofia-sip,xhook/sofia-sip,jart/sofia-sip,erdincay/sofia-sip,xhook/sofia-sip,erdincay/sofia-sip,erdincay/sofia-sip,xhook/sofia-sip