improve the performance for dragging around items in mrlib/graph (used by Redex's traces window and the module browser)
improve the performance for dragging around items in mrlib/graph
(used by Redex's traces window and the module browser)

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