Fix Queue -> queue, refs #38.

gevent/_threading.py

@@ -5,7 +5,10 @@ or not).
 
 This module is missing 'Thread' class, but includes 'Queue'.
 """
-from Queue import Full, Empty
+try:
+    from Queue import Full, Empty
+except ImportError:
+    from queue import Full, Empty
 from collections import deque
 import heapq
 from time import time as _time, sleep as _sleep