[34247] made the 'public' paramater of `register_taxonomy()` work by blocking
requests for non-public taxonomy archives during `parse_request()`. Blocking
taxonomy archive requests this late means that it's impossible to register an
independent query var that matches the slug of a non-public taxonomy. By
moving the block to `register_taxonomy()` - not allowing these taxonomies to
register their query vars in the first place - we free up the slug for other
use. In addition, we free up a bit of processing (no need to look for the query
var in `parse_request()` and better parallel the way non-public post types
work. See `register_post_type()`.
Non-public taxonomy archives that are requested using `?taxonomy=tax_name` are
still blocked during `parse_request`. It's only custom query vars -
`?tax_name=term` - that are affected by this change.
Props mboynes.
Fixes#21949.
git-svn-id: https://develop.svn.wordpress.org/trunk@35333 602fd350-edb4-49c9-b593-d223f7449a82
f492a81d70