Replaced grunt-mocha-hack with grunt-mocha-spawn
Got mocha-as-promised working on linux!

Had to write a crazy function to find the loaded instance of mocha.
Could consider forking mocha-as-promised and using this technique
to locate mocha. Probably worthy of a pull request.
Trying out mocha-as-promised on the beforeEach methods again.

Not sure if this will be okay on windows -- may revert this change if
instability reappears. The instability may have been the way the old
way of loading the mocha module.