rebase: report invalid commit correctly

In 9765b6ab (rebase: align variable content, 2011-02-06), the code
to error out was moved up one level. Unfortunately, one reference
to a function parameter wasn't rewritten as it should, leading to
the wrong parameter being errored on.

This error was propagated by 71786f54 (rebase: factor out reference
parsing, 2011-02-06) and merged in 78c6e0f3 (Merge branch
'mz/rebase', 2011-04-28).

Correct this by reporting $onto_name istead.
Reported-By: NManuela Hutter <manuelah@opera.com>
Signed-off-by: NErik Faye-Lund <kusmabite@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -469,7 +469,7 @@ case "$onto_name" in
 	;;
 *)
 	onto=$(git rev-parse --verify "${onto_name}^0") ||
-	die "Does not point to a valid commit: $1"
+	die "Does not point to a valid commit: $onto_name"
 	;;
 esac
 

t/t3406-rebase-message.sh

@@ -62,4 +62,9 @@ test_expect_success 'rebase -n overrides config rebase.stat config' '
         ! grep "^ fileX |  *1 +$" diffstat.txt
 '
 
+test_expect_success 'rebase --onto outputs the invalid ref' '
+	test_must_fail git rebase --onto invalid-ref HEAD HEAD 2>err &&
+	grep "invalid-ref" err
+'
+
 test_done