Imagefield widget upgrades aren't working (more complete patch)

Regarding #296195: Imagefield widget upgrades aren't working, I have worked on another solution (no web access for a while, so I didn't know the first patch existed).

Pros: creates full imagefield_widgets from old images (in essence: asks for an imagefield_widget form with default values, and completes it with whatever attributes it finds in old image), preserves base storage path (filepath) for each widget.

Cons: I'm not that a Drupal hacker, so I'm not sure my solution is respectful of Drupal's spirit. I call high-level functions (CCK ones), being confident the module is loaded, but I perhaps shouldn't.

So if someone(s) can review and try this patch (only imagefield.install is affected) on a 5.x install, I would be glad to know what issues arise.

Drupal 6.6
CCK 6.x-2.0
IF 6.x-3.0-alpha2
755 on tmp and files
download public