Gcapp.load_vec_map_ext requires that external vector map files have the same vector vocabulary as the currently running version of GC

[nlevenson]

This is a pretty aggressive contract which ensures that you're not trying to load a vector map designed to work with some other version of Ground Control. It's arguably a desirable behavior while we're learning the downstream effects of updating GC's vector vocabulary.

Is it too strict? Should we loosen it up and allow vector maps which describe a valid subset of our vector vocabulary?