fix Mac GC problem related to clipboard clients (merge to 4.2)
fix Mac GC problem related to clipboard clients (merge to 4.2)

svn: r14922

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