Revert changeset c67920d78248.
It breaks 'hg merge && hg up -c REV' when files exist only in one of the
manifests, making hg throw a traceback like:
#!/bin/sh
hg init test
cd test
echo foo > foo
hg add foo
hg commit -d '0 0' -m commit-1
echo foo >> foo
hg commit -d '1 4444444' -m commit-3
hg commit -d '1 15.1' -m commit-4
hg commit -d 'foo bar' -m commit-5
hg commit -d ' 1 4444' -m commit-6
hg commit -d '111111111111 0' -m commit-7
echo bar > bar
hg add bar
rm bar
hg commit -d "1000000 0" -m commit-8 2>&1 | sed -e "s:/.*\(/test/.*\):...\1:"
exit 0