hglib: add a __bool__ method where __nonzero__ is defined (issue4520) Python 3 uses the __bool__ magic method for determining the boolean value of an object instead of __nonzero__.

#!/usr/bin/env python

import nose
from tests import with_hg

if __name__ == '__main__':
    nose.main(addplugins=[with_hg.WithHgPlugin()])