fix race condition use of scheme_master_proc_thread in master_scheme_place
fix race condition use of scheme_master_proc_thread in master_scheme_place

svn: r12817

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