update-save-button in drscheme:unit:frame

• (send a-drscheme:unit:frame update-save-button modified?) -> void
     modified? : boolean

  This method hides or shows the save button, based on the modified? argument.

  If the save button has not been created yet, it remembers the modified? argument as an initial visiblity for the save button.

  This method is called by the set-modified method.