Implement a Static Response Cache

I was basing my code off of the 6.x version of this module (which itself was based on an old version of the ApacheSolr module). I just discovered drupal_static(), which was introduced in D7.

No use in doing our own special thing.

Patch attached. It looks like a significant change, but all I'm doing is wrapping the existing code with...

  $results = &drupal_static(__FUNCTION__);
  if (!isset($results)) {
    // Existing code...
  }

  return $results;

Other modules could get at the data by calling &drupal_static('google_appliance_parse_device_response_xml');