Update debian:squeeze for CVE-2014-4617 and debian:oldstable to add "sqeeuze-lts" (which is where new squeeze security updates are coming from)

Note that all the other commit hashes changed only because I amended the commit containing them to remove the squeeze and oldstable images so we didn't have extra bloat in our git history.

Closes #100

(See https://github.com/dotcloud/stackbrew/issues/100#issuecomment-48246143 for the `debsecan` output that prompted this.)