Added nua_prack().
Added nua_prack().

darcs-hash:20060317175305-65a35-16e6d37d99cd66b0634c66c8eab4db7824549cb2.gz

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