Removed country_code_country_list() function - now using

site_country_country_list() function provided by site_country module.
Added in a hook_form_alter() on the system_site_settings form so we can update
the country_code_country table if a new site default country is set on
admin/settings/site-information.
Now preventing users from the deleting the last (and hence default) country -
both by removing the 'delete' link and by preventing the operation.