stack: demonstrate that not reusing cached property gives different results Instead of using self._dependencies, which is a cached property, let's get fresh deps and rdeps in stack.revs method using a newly introduced stack.builddependencies method (will be removed in the next patch). This makes it easier to explain why the next patch is correct.

# name space package to host third party extensions
from __future__ import absolute_import
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)