* Added a flag `--ignore-liveness' to `nix-store --delete'. It

  deletes a path even if it is reachable from a root.  However, it
  won't delete a path that still has referrers (since that would
  violate store invariants).

  Don't try this at home.  It's a useful hack for recovering from
  certain situations in a somewhat clean way (e.g., holes in closures
  due to disk corruption).