Test Suite and Coverage for the Core Language

[vyzo]

We introduce and find latent subtle bugs in the compiler, and who knows what dark corners lurk in fringe macro uses?

We need a framework and comprehensive test suite for the core language and dialects, the expander, and the compiler itself.

[vyzo]

Prompt: fixes like this #1140 which are effectively untestable right now, for lack of framework and I don't want to haphazardly add random crap tests.