requirements: introduce constants for `shared` and `relshared` requirements
We add them to `WORKING_DIR_REQUIREMENTS` too as they should be stored in
`.hg/requires` and have information about the type of working copy.
Differential Revision: https://phab.mercurial-scm.org/D8926
# name space package to host third party extensions
from __future__ import absolute_import
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)