Replace manually activated failure tests with throw assertions

[ScottFreeCode]

Go through the test suites and find things that are failure-tests but either commented out or otherwise unusually handled and if possible change them to assert that the failure throws or passes an error to a callback or whatever the expectable failure mode is.

For example:

mocha/test/acceptance/fs.spec.js

Lines 17 to 18 in 2bb2b9f

	// uncomment
	// fs.readFile(tmpFile('does-not-exist'), done);