Wrap all DB creates in classloader jiggery.

Somehow opening DBs that don't use special serializers was also crashing. Fuck
if I know.

I also improved error message when a def can't be found; the blobby def id is
broken apart into its unit/id components and exported vs non-exported defs are
also handled nicely.

Now I just have to figure out why some uses are turning up that refer to
unknown defs.