Port Lua tests to busted-style tests

[SquidDev]

Historically Cobalt has been tested by running a modified version of Lua 5.1's test suite. However, this test suite isn't especially useful, for a couple of reasons:

• It's not especially granular, meaning either the whole test suite passes or you get an "assertion failed".
• It doesn't document what inconsistencies we have with PUC Lua - instead we've just got snippets of code commented out and/or changed.

To resolve this, we've been slowly fleshing out a busted-style test-suite, which can be both run against Cobalt and PUC Lua.

While we've been slowly porting tests to this new framework (e.g. 90be182), it's far from complete. We should continue this work, finally removing the AssertTest system.

This might be a good time to audit some of our test suites as well and see if we can remove some of no-longer-useful tests.