commit --amend: copy notes to the new commit

Teaches 'git commit --amend' to copy notes.  The catch is that this
must also be guarded by --no-post-rewrite, which we use to prevent
--amend from copying notes during a rebase -i 'edit'/'reword'.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t7501-commit.sh b/t/t7501-commit.sh
index 7940901..8297cb4 100755
--- a/t/t7501-commit.sh
+++ b/t/t7501-commit.sh
@@ -425,4 +425,16 @@
 
 '
 
+test_expect_success 'amend can copy notes' '
+
+	git config notes.rewrite.amend true &&
+	git config notes.rewriteRef "refs/notes/*" &&
+	test_commit foo &&
+	git notes add -m"a note" &&
+	test_tick &&
+	git commit --amend -m"new foo" &&
+	test "$(git notes show)" = "a note"
+
+'
+
 test_done