Don't disconnect on unbound prefixes.

Fixes #3083. I can't believe this was unfixed for so long, as it's
really a rather easy fix.

src/common/xmpp/dispatcher_nb.py

@@ -131,8 +131,14 @@ class Dispatcher(PlugIn):
 		if len(self._pendingExceptions) > 0:
 			_pendingException = self._pendingExceptions.pop()
 			raise _pendingException[0], _pendingException[1], _pendingException[2]
+		try:
 			try:
 				self.Stream.Parse(data)
+			except ExpatError, (e):
+				if e[0][:14] == 'unbound prefix':
+					pass
+				else:
+					raise
 			# end stream:stream tag received
 			if self.Stream and self.Stream.has_received_endtag():
 				self._owner.Connection.disconnect()