revlog.py: always return tuples from parents and parentrevs
There's at least one place doing parentrevs(rev) != (rev-1, -1),
which is always true with revlog v0, since parentrevs returns a list
in this case.
changeset: 0:9c2cf2b35aa7
user: test
date: Mon Jan 12 13:46:40 1970 +0000
summary: add foo
changeset: 1:3756a9556b89
tag: tip
user: test
date: Mon Jan 12 13:46:41 1970 +0000
summary: change foo
2 revisions:
9c2cf2b35aa7
3756a9556b89