[development] Eliminate hooks entirely in Drupal 6

[Earl Miles]

Larry Garfield wrote:
> I don't think themes themselves need to register what they override.  That 
> could be scanned and cached, too, on the theme admin page.  A theme() call 
> then just becomes a lookup to see which of the three locations, in order, a 
> theme file exists.  Just borrow some of chx's menu magic SQL to find 
> the "right" template.

I'm not completely sure that scanning would be adequate here; but I'm also not 
sure it wouldn't be. This will need to be analyzed, I think.

For example, code that changes templates on some condition needs to be 
retained, and scanning might break this. I'm not sure, scanning might be able 
to take it into account in some fashion.