[Cuis-dev] Enable state for pluggable button

[ken.dickey at whidbey.com]

Also note

   EnableDisableButton class

in 'Morphic-Games-Solitaire' package

which grays/darkens a button when disabled and answers 'false' to 
#handlesMouseDown: in this case.

Would it be better to have a FancyPluggableButtonMorph subclass or 
refactor the current PluggableButtonMorph ?

-KenD