sip_session: print info on SIPAccountRegistrationDidSucceed/DidFail/DidEnd

darcs-hash:20090408090027-b2873-4dea7eddcc57c0fd351e3f8d65a8cbddeea2287e
sip_session: fix typo in :help

darcs-hash:20090408090421-b2873-7bca94513b952b6d7adb70cfa20d05f8bcaf4a9d