Allow autocomplete to change URIs after onload

The autocomplete widget creates two objects, an ACDB and a jsAC. The ACDB reference is handed to jsAC and contains a reference to the URI to contact to get the autocomplete information. However, the jsAC is created and it's reference is thrown away when this line is run in autocompleteAutoAttach():

new jsAC(input, acdb[uri]);

I would like to suggest that this reference be attached to a variable that can be later modified, i.e.:

autocomplete_fields['edit-foo'].db.uri = 'http://example.com/new/auto/uri'

With this solution, a helper method might be nice, e.g.:

autocomplete_fields['edit-foo'].db.setUri('http://example.com/new/auto/uri')

Another alternative would be to store a reference to the original autocomplete input and use the value stored in the field rather than an internal variable. This would allow customizations like this:

document.getElementById('edit-foo-autocomplete').value = 'http://example.com/new/auto/uri'

I have a page that contains a select list that updates an autocomplete field based upon the most recent selection. As is, I've hacked the autocomplete.js so that it stores the autocomplete_fields as described. I've attached the patch that I've been using, which is just the very simple implementation of the first strategy.