What’s a romantic comedy to do when it is neither romantic nor comedic? When that film is “Admission,” it plunges forward drunkenly, hoping to overcome its inadequacies with goodwill created by the cast. Thankfully for director Paul Weitz (“American Pie,” “Little Fockers”) that cast contains Tina Fey, Paul Rudd and Lily Tomlin, a group that would make a line at the post office more appealing.