AngularJS change: Add ability to handle NaNs to $watchCollection

[teropa]

Applying angular/angular.js#4605

[teropa]

Note to readers: This is added in Chapter 3, pages 76-77.

[Foxandxss]

For the ones who are up to date, the actual change is on the last else of the function:

} else {
  if (!self.$$areEqual(newValue, oldValue, false)) {
    changeCount++;
  }
  oldValue = newValue;
}

return changeCount;

This plus the test on page 76