Get the current user's twitter information with /account/verify_crede…

…ntials.

This is more robust against potentially-changing screen names.

Closes tornadoweb#51.

tornado/auth.py

@@ -723,7 +723,7 @@ def _oauth_consumer_token(self):
     @gen.coroutine
     def _oauth_get_user_future(self, access_token):
         user = yield self.twitter_request(
-            "/users/show/" + escape.native_str(access_token["screen_name"]),
+            "/account/verify_credentials",
             access_token=access_token)
         if user:
             user["username"] = user["screen_name"]