nua_stack.c: include Allow-Events in requests initiating dialog, too
nua_stack.c: include Allow-Events in requests initiating dialog, too

The Allow-Events header is now alwats included with NOTIFY requests, and
initial INVITE, SUBSCRIBE, REFER, and OPTIONS requests.

Thanks to Jerry Richards for pointing out the problem.

darcs-hash:20080519153145-65a35-deb956d7989d66c0f71545173bfc10acc32e3e7a.gz

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