Patch to make exit on Ctrl-C cleaner

From Jim Pryor

The first, "cleanup.patch", cleans up a few spots that tend to throw
exceptions for me as offlineimap is exiting from a KeyboardInterrupt.

offlineimap/threadutil.py

@@ -159,6 +159,7 @@ class ExitNotifyThread(Thread):
                             self.getName() + ".prof")
         except:
             self.setExitCause('EXCEPTION')
+            if sys:
                 self.setExitException(sys.exc_info()[1])
                 sbuf = StringIO()
                 traceback.print_exc(file = sbuf)
@@ -168,6 +169,7 @@ class ExitNotifyThread(Thread):
         if not hasattr(self, 'exitmessage'):
             self.setExitMessage(None)
 
+        if exitthreads:
             exitthreads.put(self, True)
 
     def setExitCause(self, cause):
@@ -230,6 +232,7 @@ class InstanceLimitedThread(ExitNotifyThread):
         try:
             ExitNotifyThread.run(self)
         finally:
+            if instancelimitedsems and instancelimitedsems[self.instancename]:
                 instancelimitedsems[self.instancename].release()