Clean up core.html unit tests

Cleaning up core.html unit tests...
* Use atomic (i.e. self-contained) tests.
* Fix typos that caused recently-added tests to erroneously fail.
* Consistent whitespace (tabs only).
* Always use strictEqual instead of equal, to avoid false-negatives.

All tests pass right now except the SAT overlap test, which is -13.858192987669298 instead of -18.47759. (The test was already failing before -- I didn't change anything.)

QUnit discovered a global variable creation (from forgetting "var") in collision.js, so I fixed that too.