Melissa McCarthy has earned her moment, and it is now. After scaring up an Oscar nomination for Bridesmaids and dragging The Heat and Identity Thief into the box-office winner’s circle, McCarthy gets to generate her own projects. So here’s Tammy, an unabashed vehicle for her specific strengths: She wrote it with her husband, Ben Falcone (the talented comic actor who played the air marshal in Bridesmaids), and he directed. The movie gets a mixed grade, because it doesn’t answer the central question about her talent: Can McCarthy go beyond antic co-starring roles and carry a movie as the sole lead?