Added slightly iffy state modification to prev_state = DISCONNECTING on PJSIP internally generated disconnects for Invitation

darcs-hash:20090126155422-58103-d6a78cff0123adce7b5fbf20fa26e608ddf86aa5
Corrected iffy state fix

darcs-hash:20090126162027-58103-8d6d66ab1405f302b337bd8c15ebcbdcd2395260