[PATCH] Fix bisection terminating condition

[PATCH] Fix bisection terminating condition

When testing bisection and using gitk to visualize the result, it was
obvious that the termination condition was broken.

We know what the bad entry is only when the bisection ends up telling us
to test the known-bad entry again.

Also, add a safety net: if somebody marks as good something that includes
the known-bad point, we now notice and complain, instead of writing an
empty revision to the new bisection branch.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>