requirements: add constant for revlog v1 requirement
Since this series is adding a new requirement, we might as well clean up while
we're here.
Differential Revision: https://phab.mercurial-scm.org/D10105
from __future__ import absolute_import
import hashlib
try:
from ..thirdparty import sha1dc
sha1 = sha1dc.sha1
except (ImportError, AttributeError):
sha1 = hashlib.sha1