* apt-pkg/acquire-item.cc:

* apt-pkg/acquire-item.cc:
  - remove 'old' InRelease file if we can't get a new one before
    proceeding with Release.gpg to avoid the false impression of a still
    trusted repository by a (still present) old InRelease file.
    Thanks to Simon Ruderich for reporting this issue! (CVE-2012-0214)

Effected are all versions >= 0.8.11

Possible attack summary:
- Attacker needs to find a user which has run at least one successful
 'apt-get update' against an archive providing InRelease files.
- Create a Packages file with his preferred content.
- Attacker then prevents the download of InRelease, Release and
  Release.gpg (alternatively he creates a valid Release file and sends
  this, the other two files need to be missing either way).
- User updates against this, getting the modified Packages file without
  any indication of being unsigned (beside the "Ign InRelease" and
  "Ign Release.gpg" in the output of 'apt-get update').
=> deb files from this source are considered 'trusted' (and therefore the
   user isn't asked for an additional confirmation before install)