Twisted use of pygtkcompat breaks support of old pygobject APIS

This happens now, at least in tests, thanks to the new twisted in Ubuntu 13.04 using pygtkcompat:

Traceback (most recent call last):
  File "/usr/bin/u1trial", line 40, in <module>
    main()
  File "/usr/lib/python2.7/dist-packages/ubuntuone-dev-tools/ubuntuone/devtools/runners/__init__.py", line 277, in main
    suite = test_runner.get_suite(options)
  File "/usr/lib/python2.7/dist-packages/ubuntuone-dev-tools/ubuntuone/devtools/runners/__init__.py", line 173, in get_suite
    config['ignore-paths']))
  File "/usr/lib/python2.7/dist-packages/ubuntuone-dev-tools/ubuntuone/devtools/runners/__init__.py", line 157, in _collect_tests
    module_suite = self._load_unittest(filepath)
  File "/usr/lib/python2.7/dist-packages/ubuntuone-dev-tools/ubuntuone/devtools/runners/__init__.py", line 98, in _load_unittest
    module = __import__(modpath, None, None, [""])
  File "/mnt/tarmac/cache/ubuntuone-client/trunk/tests/platform/os_helper/test_linux.py", line 39, in <module>
    GIO_NOT_SUPPORTED = gio.ERROR_NOT_SUPPORTED
  File "/usr/lib/python2.7/dist-packages/gi/module.py", line 316, in __getattr__
    return getattr(self._introspection_module, name)
  File "/usr/lib/python2.7/dist-packages/gi/module.py", line 135, in __getattr__
    self.__name__, name))
AttributeError: 'gi.repository.Gio' object has no attribute 'ERROR_NOT_SUPPORTED'

This is because we check for the old API being loaded first, and use gi only when it isn't in use. However, use of pygtkcompat in twisted's gireactor now, means that the things we were checking for are set in sys.modules, but actually point to the new APIs, which are not compatible.