hg push sometimes doesn't require --force when it should when using --rev.

hg init t1
cd t1
echo a > a
cd ..
hg clone t1 t2
cd t2
echo b > b
hg branch foo
hg ci -Am m
hg up default
echo c > c
hg ci -Am m
hg merge foo
hg ci -m m
echo cc > c
hg ci -Am m
hg out
hg push # should require --force
hg out -r 3
hg push -r 3 # shouldn't work without --force, since it adds a new branch