sequencer: make refs generated by the `label` command worktree-local

This allows for rebases to be run in parallel in separate worktrees
(think: interrupted in the middle of one rebase, being asked to perform
a different rebase, adding a separate worktree just for that job).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -600,7 +600,8 @@ int dwim_log(const char *str, int len, struct object_id *oid, char **log)
 static int is_per_worktree_ref(const char *refname)
 {
 	return !strcmp(refname, "HEAD") ||
-		starts_with(refname, "refs/bisect/");
+		starts_with(refname, "refs/bisect/") ||
+		starts_with(refname, "refs/rewritten/");
 }
 
 static int is_pseudoref_syntax(const char *refname)

t/t3430-rebase-merges.sh

@@ -176,4 +176,18 @@ test_expect_success 'with a branch tip that was cherry-picked already' '
 	EOF
 '
 
+test_expect_success 'refs/rewritten/* is worktree-local' '
+	git worktree add wt &&
+	cat >wt/script-from-scratch <<-\EOF &&
+	label xyz
+	exec GIT_DIR=../.git git rev-parse --verify refs/rewritten/xyz >a || :
+	exec git rev-parse --verify refs/rewritten/xyz >b
+	EOF
+
+	test_config -C wt sequence.editor \""$PWD"/replace-editor.sh\" &&
+	git -C wt rebase -i HEAD &&
+	test_must_be_empty wt/a &&
+	test_cmp_rev HEAD "$(cat wt/b)"
+'
+
 test_done