show: --ignore-missing

Instead of barfing, simply ignore bad object names seen in the
input. This is useful when reading from "git notes list" output
that may refer to objects that have already been garbage collected.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rev-parse.c

@@ -44,6 +44,7 @@ static int is_rev_argument(const char *arg)
 		"--branches=",
 		"--branches",
 		"--header",
+		"--ignore-missing",
 		"--max-age=",
 		"--max-count=",
 		"--min-age=",