python3: Queue -> queue

import queue (python3) if Queue is not available (python2)

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

offlineimap/ui/UIBase.py

@@ -22,7 +22,10 @@ import sys
 import os
 import traceback
 import threading
-from Queue import Queue
+try:
+    from Queue import Queue
+except ImportError: #python3
+    from queue import Queue
 from collections import deque
 from offlineimap.error import OfflineImapError
 import offlineimap