try close method to close FDs in IOLoop

If an object has a `close` method, use that first,
then fallback on `os.close`.

This is useful in subclasses that support polling things (zmq sockets, specifically)
that are not simple FDs (and Jython, I hear?).

tornado/ioloop.py

@@ -505,7 +505,10 @@ def close(self, all_fds=False):
         if all_fds:
             for fd in self._handlers.keys():
                 try:
-                    os.close(fd)
+                    try:
+                        fd.close()
+                    except AttributeError:
+                        os.close(fd)
                 except Exception:
                     gen_log.debug("error closing fd %s", fd, exc_info=True)
         self._waker.close()