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

mkdir t
cd t
hg init
echo a > a
hg add a
hg commit -m test -d "1000000 0"
hg history
hg manifest
hg cat a
hg verify