Fix the broken thread debugging

Using threading._VERBOSE=1 is broken since python 2.6 till at least
python 3.2, (http://bugs.python.org/issue4188) so we can't use it for
our thread debugging.

Remove the usage of threading._VERBOSE, and implement a "light thread
debug log" that for now outputs information when a new thread is being
registered and when it is being unregistered. I am sure we will be able
to add more thread debugging information over the time.

Besides '-d thread' this will re-enable the usage of -d 'all' for the
most verbose debugging of all categories.

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

Changelog.draft.rst

@@ -21,6 +21,7 @@ Changes
 Bug Fixes
 ---------
 
+* Fix the offlineimap crash when invoking debug option 'thread'
 
 Pending for the next major release
 ==================================

offlineimap/init.py

@@ -226,8 +226,6 @@ class OfflineImap:
                 ui.add_debug(type)
                 if type.lower() == 'imap':
                     imaplib.Debug = 5
-                if type.lower() == 'thread':
-                    threading._VERBOSE = 1
 
         if options.runonce:
             # FIXME: maybe need a better

offlineimap/ui/UIBase.py

@@ -89,11 +89,14 @@ class UIBase:
                   (threading.currentThread().getName(),
                    s.getthreadaccount(s), account)
         s.threadaccounts[threading.currentThread()] = account
+        s.debug('thread', "Register new thread '%s' (account '%s')" %\
+                    (threading.currentThread().getName(), account))
 
     def unregisterthread(s, thr):
         """Recognizes a thread has exited."""
         if s.threadaccounts.has_key(thr):
             del s.threadaccounts[thr]
+        s.debug('thread', "Unregister thread '%s'" % thr.getName())
 
     def getthreadaccount(s, thr = None):
         if not thr: