Options for better user experience with province selection, look into better cache solution too

We're in beta-test of a site that uses addresses as part of a content profile in a few places. We have received pretty consistent negative feedback that stems from the delayed 'pop-up' nature of the provinces select box, and so we made some changes as reflected in the attached patch to address this. In particular:

1. always display a throbber when country is selected and the JSON call is made to retrieve provinces,
2. optionally add a "-- Please Select --" to the top of the provices select list when the list is returned to the browser,
3. optionally have the province list always show even if no country is selected yet by initially having a single option of "Choose a country first",
4. properly passing back error and required flags to the _addresses_provice_ajax function so that the 'required' and 'error' classes can be correctly added to the controls sent back to the browser, and
5. wrapping the country element div and the new throbber div in an overall div so that the trobber can appear behind the country selector via css and javascript.

The attached patch borrows some ideas from More robust JavaScript to allow form theming, and also includes the following fixes:

1. customising field labels for parts of the address,
2. removing the check_plain function call from function theme_addresses_aname, as that call was causing things like apostrophies to appear as hex codes,
3. ensuring the proper label is passed to the js for province, and
4. improving the formatting of single-line display.