fixed auth.impersonating again, thanks Ricardo

VERSION

@@ -1 +1 @@
-Version 2.1.1 (2012-10-16 10:54:30) dev
+Version 2.1.1 (2012-10-16 11:08:39) dev

gluon/tools.py

@@ -2746,7 +2746,8 @@ class Auth(object):
                     callback(form)
             log = self.messages.impersonate_log
             self.log_event(log,dict(id=current_id, other_id=auth.user.id))
-        elif user_id in (0, '0') and self.is_impersonating():
+        elif user_id in (0, '0'):
+            if self.is_impersonating():
                 session.clear()
                 session.update(cPickle.loads(auth.impersonator))
                 self.user = session.auth.user