gtk: change clipboard access to keep racket in charge  instead of letting the ... _wait_...() function drive an  event loop;  hopefully Closes PR 11534
gtk: change clipboard access to keep racket in charge
 instead of letting the ... _wait_...() function drive an
 event loop;
 hopefully Closes PR 11534

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