EVANSTON—Donning a fresh new suit, an American flag pin, and a Bill Clinton mask, McCormick sophomore Shane Feinberg strolled out of Allison Hall a confident man Saturday night.  He was 0 for 13 so far in his Northwestern flirting career, but there was no doubt in his mind that Saturday would be the night a female would rendezvous with his slick Willie. For that night he was not Shane Feinberg, the awkward Jewish kid whose greatest scores had come on calculus