#674772 by joachim: Unable to distinguish profile.module fields with same name in different profile categories.

Major re-organization of handlers. PLEASE NOTE: This drastically affected the Views module API and until modules are updated to match, they will stop working. Efforts have been made to ensure that this won't cause your site to crash, but that's partly up to the individual module as well.

Initial taxonomy implementation. There's still a ways to go -- I totally punted on depth -- and we need a few more argument handlers.