Enable US geocoding for Zip based addresses

This is a replica issue for the v5 module of this: http://drupal.org/node/117027

In an essence, it took me a lot of time to figure why the location module hasn't geocoded the US address that contain only city and zip code. I realized that the culprit is line 310 on supported/location.us.inc .

A mechanism for controlling the accepted level of accuracy is the best solution - something that would be controlled in the admin pages of the location module. If I could, I've written it and send the patch (or the like) but unfortunately, I'm too new to Drupal to write this in a reasonable amount of time.

Thanks.