RootStanza raises unexpected exceptions

We now raise the unexpected exceptions instead of sending
them on the network.
 - avoids flood (sending a traceback on a MUC, for example…) and
   maybe some security issues.
 - lets you handle the traceback (catch it to handle
   it properly, or with except_hook, etc)
 - an exception cannot be raised without you knowing

sleekxmpp/stanza/rootstanza.py

@@ -54,16 +54,17 @@ class RootStanza(StanzaBase):
                                     e.extension_args)
                 self['error'].append(extxml)
                 self['error']['type'] = e.etype
+            self.send()
         else:
-            # We probably didn't raise this on purpose, so send a traceback
+            # We probably didn't raise this on purpose, so send an error stanza
             self['error']['condition'] = 'undefined-condition'
-            if sys.version_info < (3, 0):
             self['error']['text'] = "SleekXMPP got into trouble."
-            else:
-                self['error']['text'] = traceback.format_tb(e.__traceback__)
+            self.send()
+            # log the error
             log.exception('Error handling {%s}%s stanza' %
                           (self.namespace, self.name))
-        self.send()
-
+            # Finally raise the exception, so it can be handled (or not)
+            # at a higher level
+            raise e
 
 register_stanza_plugin(RootStanza, Error)