try to be slightly smarter about invalidating the green region in the line numbers when it moves around
try to be slightly smarter about invalidating the green region
in the line numbers when it moves around

specifically, if the before and after green line are right
next to each other, then put it into a single edit sequence
(which unions the invalidated regions); if not, then we
may be jumping far away, so invalidate the two regions
and redraw them separately

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