SET-GRAPHIC-BUTTON-SENSITIVITY
==============================

syntax: (set-graphic-button-sensitivity 
           <babylon-push-button> <T | NIL>)

This function makes the Button sensitive or
insensitive. The default-value is T (sensitive).

example: >(define-task SENSITIVE-DEMO-TASK (interface)
             :documentation "This is a demo"
             actions
             (set-graphic-button-sensitivity
             (get-window-element interface "GRAPHPB1") 
             nil)
             (kb-notify "The graphic-button is 
             insensitive ?~%")
             (set-graphic-button-sensitivity
             (get-window-element interface
             "GRAPHPB1") t)
             (kb-notify "The graphic-button is
             sensitive again ?~%"))