stomp radius now with mouse, renamed partial_show_minefield()

stomp radius now with mouse, renamed partial_show_minefield()

partial_show_minefield() -> redraw_cell(): more intuitive, less long
stomp radius:
	factored out into functions show_stomp() and wait_stomp().
	initially, I just used them as-is in wait_mouse_up(), but then
	do_uncover() showed the stomp _again_, which is undesired.
	do_uncover() now takes a new parameter, actor, which tells it
	what method the user used to activate it. (feels like a dirty
	hack :( )

PS: this took 2 --amends to get right m(