Adding method to disable autorun behavior.

This adds a method which will set the `@@autorun` class variable to `false`, as well as a check that will prevent the autorun behavior if the `@@autorun` variable evaluates to false.

This enables code-level tests, which are important because most checks interact with external resources (shelling out, accessing HTTP, etc) and are best tested with mocks/stubs.  Checks are getting more complex, and multiple authors are editing individual checks, so testing is becoming more important for checks.