Functions for testing Swift fatal errors

[nhgrif]

MTK should be expanded to include tests to handle fatal errors throw in Swift without crashing the test suite.

[nhgrif]

I've looked at this CocoaWithLove article. Seems like it'll do exactly what we want to implement here, but I've been having some difficulty getting all the pieces put together correctly.

[lgauthier]

@schrismartin I know you were working on something for this. Do you think it's something we can add?