Extracted common stuff from Promises/A+ specs, for coming files.
Implemented helper to generate 3 test cases for fulfilled and rejected promises.

From https://github.com/promises-aplus/promises-tests/blob/master/lib/tests/helpers/testThreeCases.js
Added section 2.2.4 of the Promises/A+ specs. But skip for now.

I don't know how to do the execution context stack deferred stuff.