“PORN Rock: The Musical” loosened up the cast. Following their final Fringe Festival performance the other night, the actors celebrated at Madame X on West Houston Street, where the regulars won’t soon forget them. “Many danced topless,” said our source, “and writer-director Pink Snow, who starred in the show, was particularly uninhi bited and disrobed fully.” We doubt the party tonight will be as much fun. It’s the closing- night bash for “Ruined,” win ner of the 2009 Pulitzer for Drama, about the sexual op pression of women in war-torn Congo.