pop up the alert and set the error code so that the url listener doesn't try to pop up another alert. define a bunch of new error codes, and remove nsMsgTransition.h, which was defining all the MK_ error codes that were in there. are no longer needed. git-svn-id: svn://10.0.0.236/trunk@52602 18797224-902f-48f8-a5cc-f745e15eee43