outgoing: pass subrepo path using function argument instead of abssource hack
This is clearer, remove the needs for the `repo._subtoppath` hack and will make
our live easier when making `outgoing` accept multiple destinations.
Differential Revision: https://phab.mercurial-scm.org/D10390
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