* dogtail/config.py: Add new parameter: checkForA11y, which defaults
to True. If set to False, we assume accessibility is enabled.

* dogtail/utils.py: Don't import gconf until necessary.

* dogtail/tree.py, sniff/sniff: Don't check for accessibility unless
config.config.checkForA11y is True.

svn path=/trunk/; revision=391