Add support UUID support taxonomy vocabularies

The reason why I've intentionally left this out, is because vocabularies has a machine name which Features is using to export vocabularies. I consider vocabularies to be configuration because of that, and recommend using Features instead.

Basically, roles, vocabularies input formats etc, that all have machine names, should not have UUID I think.

The machine name discussion was had a long time ago. Although at the time I was in favour having roles and other things (not just entities) having UUIDs, I now see the benefits of dixon_'s approach and support it. Marking this wonfix.

I second the Entity point made in #5

What about exposing the machine_name as a UUID? We don't need to auto-generate one, because they're already unique, but not having a registered UUID for them means we can't save/load them via entity_uuid_load (which is a bit of a pain).

In my mind, it's as simple as adding the following to uuid_get_core_entity_info():

  if (module_exists('taxonomy')) {
    $info['taxonomy_vocabulary'] = array(
      'base table' => NULL,
      'entity keys' => array(
        'uuid' => 'machine_name',
      ),
    );
  }

And then tweaking a few methods in uuid.install to recognize that an empty base table means "don't provide a UUID".

Alternatively, for people looking to get entity_uuid_load to work with vocabulary machine_names, I've just added this and it seems to work. A similar pattern can be used for other entities with machine_names that aren't supported via UUID.

function MYMODULE_entity_info_alter(&$info) {
  if (!empty($info['taxonomy_vocabulary'])) {
    $info['taxonomy_vocabulary']['uuid'] = TRUE;
    $info['taxonomy_vocabulary']['entity keys']['uuid'] = 'machine_name';
  }
}

This is a very difficult discussion which have a lot of points of view, and machine_name works as local unique identifier, but not as universal, which is suppossed to be the base concept about this module.

And for me, as a developer, is a shame that extensions of a class, drops methods from base class, from my point of view, taxonomy_vocabulary extends entity.

I'm working on replicating contents between sites, and I prefer writting only one use case: clone entity, unaware of type.

An update:
Vocabularies are entities, so they can have fields, this fields can be references, so we need entity_uuid_load to make them universal.

As mentioned by @dixon_ and myself above vocabularies have machine names, so they are deemed to be configuration and supported by features not UUID. Vocabs aren't fieldable either.