Add revlog.parentrevs function.
This allows one to walk the revision graph using only revision numbers,
which can be faster than using revision hashes, especially for
RevlogNG, where the parents of a revision are stored as revision
numbers.
#!/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