Don't print error by default

[kevincox]

The code even suggests this:

snap-shot-core/src/file-system.js

Lines 260 to 261 in 0c1c912

	// QUESTION should we print the error message by default?
	console.error(fullMessage)

My test runner already has logic to capture, format and display errors. Right now I have useful logs, followed by two copies of the error and a stack trace. This pushes valuable logs and debugging information off screen and I need to go over and scroll the terminal far more often then I would if the error was only printed once.

I don't know if you want to change the default, but there should at least be an option to not print the error.