Bug#587774: Jigdos have newer timestamps than ISOs

[Mattias Wadenstein <maswan@acc.umu.se>]

Package: debian-cd
Version: 3.1.3

When generating images and jigdo files, the jigdo files sometimes end up 
with newer timestamps which in turn makes jigdo-mirror re-generate the 
image from the jigdo each and every time.

Suggested fix: touch the isos after the jigdos are done and compressed.

Additional improvement: If this works, we might add a cron:ed push to all 
the cd mirrors on weekly basis or so, which would be a bit more resilient 
against things like being down when the trigger after a new release gets 
sent out, etc.

/Mattias Wadenstein