bisect: cleanup whitespace errors in git-bisect.sh.

All leading whitespace is now encoded with tabs.

After this patch, the following is true:

	RAW=$(cat git-bisect.sh | md5sum) &&
	ROUNDTRIP=$(cat git-bisect.sh | expand -i - | unexpand --first-only - | md5sum) &&
	LEADING=$(sed -n "/^  */p" < git-bisect.sh | wc -l) &&
	test $RAW = $ROUNDTRIP &&
	test $LEADING = 0 &&
	test -z "$(git diff -w HEAD~1 HEAD)"
Signed-off-by: NJon Seymour <jon.seymour@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>