Sets the grayed state of the checkbox for this item. This state change
only applies if the Tree was created with the SWT.CHECK style.
@param grayed the new grayed state of the checkbox
@exception SWTException <ul>
<li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
<li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
</ul>
Sets the grayed state of the checkbox for this item. This state change only applies if the Tree was created with the SWT.CHECK style.
@param grayed the new grayed state of the checkbox
@exception SWTException <ul> <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li> <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li> </ul>