narrow: add support for merging add and remove outside of the tracked set
This extend f1eb77dceb36 to test and support the remaining action. Or, at least,
the simple incarnation of them.
Differential Revision: https://phab.mercurial-scm.org/D12181
# name space package to host third party extensions
from __future__ import absolute_import
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)