Re-deleted exc_clear. Reason:

 - It's unnecessary
 - It confuses people

See [7433] and #1575. This is an old workaround for psyco braindeadness, which
we don't use anymore. If there's a reason this should stay in code, please
document clearly, and re-add. Thanks.

src/common/xmpp/dispatcher_nb.py

@@ -135,7 +135,6 @@ class Dispatcher(PlugIn):
 				self._owner.Connection.disconnect()
 				return 0
 		except ExpatError:
-			sys.exc_clear()
 			self.DEBUG('Invalid XML received from server. Forcing disconnect.', 'error')
 			self._owner.Connection.pollend()
 			return 0