Always show full tracebacks at the end of the run

This greatly simplifies developer's life and will, possibly, allow
users familiar with Python to debug and fix the problems by
themselves.

We, possibly, should not give tracebacks for the problems like
"can't open connection", but this is up to the caller of this
routine not to provide traceback in this case.

Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>

offlineimap/ui/UIBase.py

@@ -124,6 +124,11 @@ class UIBase(object):
         of the sync run when offlineiamp exits. It is recommended to
         always pass in exceptions if possible, so we can give the user
         the best debugging info.
+        
+        We are always pushing tracebacks to the exception queue to
+        make them to be output at the end of the run to allow users
+        pass sensible diagnostics to the developers or to solve
+        problems by themselves.
 
         One example of such a call might be:
 
@@ -135,13 +140,14 @@ class UIBase(object):
         else:
             self._msg("ERROR: %s" % (exc))
 
+        instant_traceback = exc_traceback
         if not self.debuglist:
             # only output tracebacks in debug mode
-            exc_traceback = None
+            instant_traceback = None
         # push exc on the queue for later output
         self.exc_queue.put((msg, exc, exc_traceback))
-        if exc_traceback:
-            self._msg(traceback.format_tb(exc_traceback))
+        if instant_traceback:
+            self._msg(traceback.format_tb(instant_traceback))
 
     def registerthread(self, account):
         """Register current thread as being associated with an account name"""