gitlog: fix embarassing bug that prevented log from showing correct parents
We had the correct parents in the database, but the changelog was
always returning p1 for all parents. Oops.
Differential Revision: https://phab.mercurial-scm.org/D8263
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL