clean up ascii art => unicode a little
clean up ascii art => unicode a little

adjust the way it changes characters so it
doesn't change them when they are already the right
thing (this means set-modified is not always called
and also improves performance in the case that little
changes in a big diagram)

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket