Use Py2/Py3 compatible exception catching syntax

New syntax "as ex" was introduced in Python 2.6
and is the only one supported in Python 3.x.

See, http://legacy.python.org/dev/peps/pep-3110/
Use Py2/Py3 compatible octal number syntax

See, http://legacy.python.org/dev/peps/pep-3127/#removal-of-old-octal-syntax
Make zope interfaces declarations Py3 compatible
Use print as function
Use Py2/Py3 compatible StringIO import
Initial support for DBus method invocation on Python3

  Things fixed:
  * one of authentication flows (not sure which ones, but it works :))
  * message sending and parsing sufficient to call the method

  The example app works on Twisted 14.0.1 with the patch from
  https://twistedmatrix.com/trac/ticket/6466 applied.
Merge pull request #16 from madkinder/python3

A bit of Python3 support. Compliments of madkinder.