cleanup import statements and conform to PEP-8

Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/folder/UIDMaps.py

@@ -17,10 +17,8 @@
 #    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 
 from threading import *
-from offlineimap import threadutil
-from offlineimap.threadutil import InstanceLimitedThread
 from IMAP import IMAPFolder
-import os.path, re
+import os.path
 
 class MappingFolderMixIn:
     def _initmapping(self):