calendar pop-up icon doesn't visually disable

Some forms have a date entry field that can be enabled and disabled via a checkbox.

When disabled, the calender icon to use the pop-up selector remains blue (or the standard theme link color) rather than being grayed out like the other parts of the control, even though it is actually disabled and can't be used.

This could be changed by adding/removing the "disabled" class to the <a> tag as the control enables/disables.

There is already code to add the cursor style default as inline styles, which becomes unnecessary as a.disabled in Bootstrap does this as well.