Merge apt--mvo--0

Merge apt--mvo--0
Patches applied:

 * michael.vogt@ubuntu.com--2005/apt--mvo--0--patch-9
   * be more carefull when building the archive path (thanks to matt!)

 * michael.vogt@ubuntu.com--2005/apt--mvo--0--patch-10
   * ignore time conflicts on apt-key update (this is used at install time when the clock may be totally broken)

 * michael.vogt@ubuntu.com--2005/apt--mvo--0--patch-11
   * run check_size_constraints independent of AUTOCLEAN (thanks Matt)

 * michael.vogt@ubuntu.com--2005/apt--mvo--0--patch-12
   * check cache size after AUTOCLEAN was run (but independent)

 * michael.vogt@ubuntu.com--2005/apt--mvo--0--patch-13
   * MinAge implemented, cron script variables documented, bugfix in check_stamp() function