When Nilo Cruz got the phone call informing him that his new play, Anna in the Tropics, had won the Pulitzer Prize for drama, he wasn’t entirely sure if he believed it. After all, he was a little-known playwright whose play had only been seen onn stage during a short run in Florida, and he was up against such legends as Edward Albee and Richard Greenberg, both of whose entries were running in New York. But it was no joke: Cruz is the first Latino playwright to win the prize, and his play gets a more auspicious bow this week at the McCarter Theatre in Princeton, before moving to Broadway later in the fall.