This is required for a bugfix for ocamldoc to support the -open flag.

[ci skip]

* Test for __$ERROR__ global variable set by prelude.
* Tests return result for thrown exceptions and test's @negative status.

Use setImmediate instead of the before hook, so it does not have to be
triggered for the test suite to be loaded.

Fixes #1

Revisit floating point equality. Swap all direct comparisons for pos/neg 0 and NaN with specific functions.