git bisect should return 1 when the first bad commit is found

Hi

I'm using git bisect, and for complex reasons I can't use git bisect
run to drive the bisection. I don't think git bisect bad/good is
returning a different status code when the first bad commit is found
and this would be very useful to stop the driver of the bisection.

What do you think?  Would such a change be acceptable?

Thank you!

Pedro.