Curtis Sliwa, for 18 years one of the most recognizable and persistent voices on WABC (770 AM), is leaving the station. WABC Tuesday announced that as of Monday, John Batchelor will begin hosting the 9 p.m.-1 a.m. weeknight slot that Sliwa had been holding down. Sliwa, also known as the founder of the Guardian Angels, confirmed Tuesday that "WABC and I were not able to agree on an extension of my contract." Concerning reports that he is talking with WNYM (970 AM), "The Apple," Sliwa said, "nothing is signed." For now, he said, he will continue to broadcast nightly from...