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:
adding baseabort: cannot delete applied patch cNow at: bababseriesstatusNow at: aabseriesstatus1 New patch: a0 baseabort: patch e not at basef4 New patch: f3 New patch: e2 New patch: d1 New patch: a0 base