An extra bit of diag on incomplete rsrc re-register

An extra bit of diag on incomplete rsrc re-register

Due to the counterintuitive nature of the metadata subsystem, a user wishing
to modify the metadata for a result class at runtime (post $schema instance
initialization), may end up in a situation where *everything* appears to work
but falls apart on the next call to My::Schema->connect. In fact I myself made
this very mistake in https://github.com/ctrlo/GADS/pull/1/files, even though
I was pretty well aware of the dangers at the time.

In order to make this go away for good reuse the meta-metadata kept around to
track rsrc ancestry and modifications, and emit a warning alerting folks to
the potential problem (the *actual* problematic desync will also be warned
about at a later step by the stale-metadata diag).