copies: extract function for deciding whether to use changeset-centric algos
We'll eventually have a "experimental.copies.read-from=changeset-only"
option too and I don't want to spread the logic for determining if we
should use changeset-centric of filelog-centric algorithms.
Differential Revision: https://phab.mercurial-scm.org/D6163
# name space package to host third party extensions
from __future__ import absolute_import
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)