* (bug 12723) OpenSearch description name now uses more compact language code

* (bug 12723) OpenSearch description name now uses more compact language code
  to avoid passing the length limit as often, is customizable per site via
  'opensearch-shortname' message.

Note that the spec actually says ShortName should be trimmed to *16* chars,
which is pretty awful -- 'Wikimedia Commons' doesn't even fit. I haven't
changed the current trimming (to 24 characters).

Note that Firefox uses the longer 'Description' field for its 'add' menu
item, but the ShortName for the actual item once you add it to the menu.

Possibly should have separate description and shortname thingies and do some
smarter trimming. Sigh.