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.
#!/bin/sh
hg init
echo foo > a
hg add a
hg commit -m "1" -d "1000000 0"
hg verify
chmod -r .hg/data/a.i
hg verify 2>/dev/null || echo verify failed
chmod +r .hg/data/a.i
hg verify 2>/dev/null || echo verify failed
chmod -w .hg/data/a.i
echo barber > a
hg commit -m "2" -d "1000000 0" 2>/dev/null || echo commit failed