[Soc2014] Official meta API

I find `parent_model` to be a rather confusing name. As best I can figure out, it means the "other model" for a related field. Is that right?

If that's the case, it seems to me that

a) a name like `related_model` would be a lot clearer than `parent_model` (we don't usually use parent/child terminology to talk about foreign-key or similar relationships), and

b) It should be `None`, not the same as `model`, for a non-related field. It doesn't make any sense to say that the `related_model` (or `parent_model`) for a `CharField` is the model the `CharField` is on.