Annotate was being too clever trying to work in place, and triggering
its assert. Simplify it, fix it, and speed it up a tiny bit.
set -ex
export EDITOR=true
rm -rf test branch
mkdir test
cd test
echo foo>foo
hg init
hg addremove
hg commit
hg verify
cd ..
cp -a test branch
cd branch
echo bar>>foo
hg commit
cd ../test
hg merge ../branch
hg verify