[Soc2014] Official meta API

On closer inspection, this might be less of an issue than I originally thought. 

If this was a public method, I'd completely agree that we should find the underlying concept and name it. 

However, this is an internal method for the admin, because of a subtle change in the return values for `get_fields()`. Admin doesn't handle GFK fields, so they need to be excluded. This isn't public API; it's an implementation detail of the admin where a specific limitation of admin needs to be accounted for.

If we wanted to avoid the GFK name, we'd end up doing a dance around a name like "multimodel_relation" or some similar alternate name for GFK - because it really is GFKs that are the problem here. The internal code doesn't use any "is_GFK" checks - it checks to see if the field is a relation and has no related_model - but for convenience, since a GFK is the only field that is likely to meet that criteria, the wrapper method uses the name 'gfk'.