obshash: properly cache obshash value The code was buggy and only cached non-nullid/non-inherited value. This was previous hidden because we were using a 'propertycache' to cache the value on the range object. This fixes it and restore a lot of performance.

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