A friendly push for a better implementation of 'taxonomy_override_selector'

I thought that I would see if I could get your support to push this last minute request in Changes to the taxonomy_override_selector settings. This is 1 week over the code freeze. (thus the critical flag)

It adds a flag on each vocab for 'taxonomy_override_selector', so you would never every need to re-implement the core term selector again!! Anyway have a quick review, see if it meets your requirements and bump it in a couple of days to push it back up the queue ;)

I wanted to rip the free-tagging and standard selects into external functions to make things even easier for us, but the change could be too big for inclusion at this late stage.

Cheers

Alan