If a session was terminated because of a error response returned to a
request (as specified by RFC 5157), the nua_i_state event was not sent.

Even with this fix, if a dialog has multiple usages, the event usages can be
terminated without any indication to the application.

darcs-hash:20080307163336-65a35-cd2e979af405323e2131c7c8dc662e0ab645bbac.gz