Added assertions guarding against invalid use of the nua_glib API.
Added assertions guarding against invalid use of the nua_glib API.

darcs-hash:20060913142233-7659e-f6ee55ccfddfd4a06566669872ae80f5fd45d4cd.gz

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