path: add a new argument to control path validation
During pull, unvalidated path might be used, having the option to do so directly will allow use to simplify some code and unlock more `path` usage later in the series.
Differential Revision: https://phab.mercurial-scm.org/D11671
# name space package to host third party extensions
from __future__ import absolute_import
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)