Only harmonizing if we need to... allows debugging to be possible

See description on [stackoverflow question here](http://stackoverflow.com/questions/25142173/debugging-jest-test-cases-using-node-inspector/26415442#26415442)

Created [github issue here](https://github.com/facebook/jest/issues/152)

It seems the `harmonize` module already does this (albeit in a slightly different way):
https://github.com/dcodeIO/node-harmonize/blob/master/harmonize.js#L25