proxypass & HTTP_X_FORWARDED_HOST

When Drupal is served through a proxy (Apache proxypass) gmap_get_key function must be rewritten. This is a generic solutions in both cases:

function gmap_get_key() {
  $key = variable_get('googlemap_api_key', '');
  if (module_exists('keys_api')) {
    $key = keys_api_get_key('gmap', $_SERVER["HTTP_X_FORWARDED_HOST"]? $_SERVER["HTTP_X_FORWARDED_HOST"] : $_SERVER["HTTP_HOST"]);
  }
  return $key;
}