Following 'enum bisect_error' vocabulary, return variable 'res' is
always non-positive.
Let's use '-res' instead of 'abs(res)' to make the code clearer.

Mentored-by: Christian Couder [off-list ref]
Signed-off-by: Miriam Rubio <redacted>
Helped-by: Junio C Hamano [off-list ref]

Although there is no set rule for this, but I think that your sign-off
goes at the last generally. This is what I have seen on various patches.