bisect--helper: `is_expected_rev` & `check_expected_revs` shell function in C

bisect--helper: `is_expected_rev` & `check_expected_revs` shell function in C

Reimplement `is_expected_rev` & `check_expected_revs` shell function in
C and add a `--check-expected-revs` subcommand to `git bisect--helper` to
call it from git-bisect.sh .

Using `--check-expected-revs` subcommand is a temporary measure to port
shell functions to C so as to use the existing test suite. As more
functions are ported, this subcommand would be retired but its
implementation will be called by some other method.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Mentored-by: Lars Schneider <larsxschneider@gmail.com>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Pranit Bauva <pranit.bauva@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>