python3: import absolute package name

This import failed in python3, we need to either specify "." (relative) or
from OfflineImap.ui. (absolute). Done the latter.

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

offlineimap/ui/Machine.py

@@ -17,8 +17,8 @@ from urllib import urlencode
 import sys
 import time
 import logging
-from UIBase import UIBase
 from threading import currentThread
+from offlineimap.ui.UIBase import UIBase
 import offlineimap
 
 protocol = '7.0.0'