Refactor drupal.js

There's broad interest among Drupal Javascript developers in refactoring our drupal.js library. From http://groups.drupal.org/node/603:

Drupal 4.7 introduced a slim and well designed set of Javascript utility functions (drupal.js) and behaviors (autocomplete, collapse, etc.). As Drupal contributors continue to develop Javascript and AJAX behaviors, there is an emerging consensus around ways we could make Drupal's Javascript library more readily extensible while solving issues such as namespace collisions. There is also interest in the possibility of adopting or piggybacking on one of the several leading Javascript/AJAX utility libraries (jQuery, Prototype, etc.).

This initiative may develop into a Drupal Enhancement Proposal. There's also a proposal to develop a proposed solution via a new group at http://groups.drupal.org/drupal-js.

After we work through those discussions and processes, we can post proposed changes here.