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
echo "[extensions]" >> $HGRCPATH
echo "mq=" >> $HGRCPATH
hg init a
cd a
echo 'base' > base
hg ci -Ambase -d '1 0'
hg qnew -mmqbase mqbase
hg qrename mqbase renamed
mkdir .hg/patches/foo
hg qrename renamed foo
hg qseries
ls .hg/patches/foo
mkdir .hg/patches/bar
hg qrename foo/renamed bar
hg qseries
ls .hg/patches/bar
hg qrename bar/renamed baz
hg qseries
ls .hg/patches/baz