bisect: report bad rev better

The previous one overwrote the variable used to report the bad input
when the input is actually bad, and we did not give a useful enough
information.  This corrects it.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-bisect.sh

@@ -155,9 +155,9 @@ bisect_state() {
 		shift
 		for rev in "$@"
 		do
-			rev=$(git rev-parse --verify "$rev^{commit}") ||
+			sha=$(git rev-parse --verify "$rev^{commit}") ||
 				die "Bad rev input: $rev"
-			bisect_write "$state" "$rev"
+			bisect_write "$state" "$sha"
 		done ;;
 	*,bad)
 		die "'git bisect bad' can take only one argument." ;;