Since we want to get rid of git-bisect.sh, it would be necessary to
convert those exit() calls to return statements so that errors can be
reported.
Emulate try catch in C by converting `exit(<positive-value>)` to
`return <negative-value>`. Follow POSIX conventions to return
<negative-value> to indicate error.
Turn `exit()` to `return` calls in `bisect_checkout()`.
Changes related to return values have no bad side effects on the
code that calls `bisect_checkout()`.
Mentored-by: Christian Couder <chriscool@tuxfamily.org> Mentored-by: Johannes Schindelin <Johannes.Schindelin@gmx.de> Signed-off-by: Pranit Bauva <pranit.bauva@gmail.com> Signed-off-by: Tanushree Tumane <tanushreetumane@gmail.com> Signed-off-by: Miriam Rubio <mirucam@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>