Updated the use of tostring in xmlstream.py
Updated the use of tostring in xmlstream.py

Now uses the xmlns and stream parameters to reduce the number of
extra xmlns attributes used in the logging output.

Added self.default_ns to XMLStream just to be safe.

skinkie/SleekXMPP--XEP-0080-,destroy/SleekXMPP-gevent,EnerNOC/smallfoot-sleekxmpp