entity_revision_load() fails for entities that don't support revisions

Hi,

I ran into this issue, where entity_revision_load() is used to load a taxnomy_term with the revision id then function just return FALSE, even though the revision id DOES exist.

I found that the function checks the entity info to find the what key it's using for the revisionID, and when it fails (i.e. if the entity doesn't support revisioning), it returns false. Even though, technically speaking, that one version of the taxonomy_term is still a revision (even if it's the only revision), and I would expect the function to still return it.

The function description says it would return FALSE "if there is no entity with the given revision id."... which is not the case here.

I will attach a simple patch to add that bit of logic.