William P. Garvey, the 68-year-old president of Mercyhurst College, has long prided himself on the 17 years he coached grade-school basketball in Erie from the late 1950s through the mid-1970s.But Garvey, according to one of his former players, was something other than a coach and mentor.He was also a sexual predator, the former player said.In a newly published memoir and a June 2002 column in the