removing 'checked' attr from input[type="radio"] when setting value is different from el.val()

Now behaviour will be similar to input[type="checkbox"].
This will allow correct behaviour with radios when calling model.unset
or model.set with value not existing in radios - after this operations
none radio will be checked.
Merge pull request #67 from kubelsmieci/input.radio-removeAttr.checked-whenValueNotEqual

removing 'checked' attr from input[type="radio"] when setting value is d...