tests: Ditch the python test framework, use standard make check with a small

tests: Ditch the python test framework, use standard make check with a small
set of JavaScript functions to deal with assertions and unreachable code
and whatnot. Also, clean up some tests, and remove some that made no sense
whatsoever.

Three or four tests still don't work (and print output to that effect)
because of strange exception-chaining problems which I'm going to look into.