'git bisect visualize'

'git bisect visualize'

Linus says:

    I'm testing bisection to find a bug that causes my G5 to no longer boot,
    and during the process have found this command line very nice:

	    gitk bisect/bad --not $(cd .git/refs ; ls bisect/good-*)

    it basically shows the state of bisection with the known bad commit as the
    top, and cutting off all the good commits - so what you see are the
    potential buggy commits.

Signed-off-by: Junio C Hamano <junkio@cox.net>