redesign testing

[nikodemus]

Current tests take way too long to run.

Basic plan: instead of invoking the compiler or interperter a million times, run foo/tests/test.foo just once in each mode -- host system, evaluator, and compiled.

Then make sure test_foolang.foo stuff, etc, is covered there -- as toplevel classes for the most part.

• migrate tests from test.foo to self_test.foo, run on target #835
• Consolidate tests #841
• run self_test.foo on host as well, replacing test.foo entirely #842

[nikodemus]

Plan is good, breakdown exists, no need to keep this.