Update activeselect module for 5.0

Here's a patch to upgrade activeselect to 5.0. Unsurprisingly, the really big thing that this patch caters for is the addition of jQuery in Drupal 5. This patch has been tested with the 5.0-patched version of the category module (see http://drupal.org/node/85239 for the category module upgrade patch), and while the category module's hook_activeselect implementation still needs some work, activeselect itself seems to be working pretty well.

For the new .info file, I haven't put activeselect into a package. Does anyone know if there are plans to have all JS util modules under a 'JavaScript' package? If so, I will make activeselect part of such a package. Otherwise, I will just leave its package unspecified.

The 4.7 activeselect.js code was based on the 4.7 autocomplete.js code, and as such, the 5.0 update is mainly based on the changes made to the core autocomplete.js code for 5.0. As with autocomplete, despite jQuery the JS code hasn't actually changed that much.

I think this patch is fairly stable, but testing and feedback is of course welcome.

Patch committed to HEAD, and new Drupal 5 branch of activeselect created.