makefile: add a build-chg option
This is done as a gratuitous improvement on the way to add makefile entry to
build and install rhg.
It seems saner to have equivalent entry for chg too.
Differential Revision: https://phab.mercurial-scm.org/D10191
# name space package to host third party extensions
from __future__ import absolute_import
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)