largefile: use `parentchange` during rollback
rollback is updating parent without touching the working copy. It should wrapped
in a `parentchange` context.
Differential Revision: https://phab.mercurial-scm.org/D11108
from __future__ import absolute_import
import hashlib
try:
from ..thirdparty import sha1dc # pytype: disable=import-error
sha1 = sha1dc.sha1
except (ImportError, AttributeError):
sha1 = hashlib.sha1