Add cache headers and drupal_exit in the return of taxonomy autocomplete function.

I have noticed, that output of taxonomy autocomplete dont have cache headers.
When user try to find taxonomy term name he often in puts equal data in autocomplete field.

For example, I'm very often write "test" word and then delete some symbols and try another word.
DB at that time receive different queries with like:
t
te
tes
test
tes
te
ter
terr

As You can see there are many equal requests to the backend in little period of time.
I'm proposing to make return of the function like this:

 drupal_add_http_header('Cache-Control', 'public, max-age=' . variable_get('cache_lifetime', 300));
 drupal_json_output($term_matches);
 drupal_exit();

In this case we will reduce requests count to db storage during autocomplete action.