Potential fix for issue #193

This fix for #193 will cause the ```errorElementClass``` to be applied to all ```<input type="radio" />``` elements that are bound using the ```checked``` binding, but I'm not convinced that this is definitely the desired behaviour.

If you view (this example)[http://jsfiddle.net/stevegreatrex/qsLvS/2/] you can see it working but it causes the error message to be appended to every input, which doesn't necessarily make sense.

You could work around this by using ```validationOptions``` to enable/disable the ```decorateElement``` behaviour for a specific area though.