title: Disabling code coverage for guard spec runs
body: <p>For a variety of reasons, I find that running code coverage every time my files reload from guard is quite a burden. However, there doesn't seem to be a way to conditionally prevent SimpleCov from starting from the spec helper.</p>
  
  <p>Is there a way to disable SimpleCov when run by guard, but not when I run it normally using <code>rake spec</code>?</p>