refs: make refs/bisect/* per-worktree

We need the place we stick refs for bisects in progress to not be
shared between worktrees.  So we make the refs/bisect/ hierarchy
per-worktree.

The is_per_worktree_ref function and associated docs learn that
refs/bisect/ is per-worktree, as does the git_path code in path.c

The ref-packing functions learn that per-worktree refs should not be
packed (since packed-refs is common rather than per-worktree).

Since refs/bisect is per-worktree, logs/refs/bisect should be too.

Signed-off-by: David Turner <dturner@twopensource.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

path.c

@@ -107,9 +107,11 @@ static struct common_dir common_list[] = {
 	{ 0, 0, 1, "info/sparse-checkout" },
 	{ 1, 1, 0, "logs" },
 	{ 1, 1, 1, "logs/HEAD" },
+	{ 0, 1, 1, "logs/refs/bisect" },
 	{ 0, 1, 0, "lost-found" },
 	{ 0, 1, 0, "objects" },
 	{ 0, 1, 0, "refs" },
+	{ 0, 1, 1, "refs/bisect" },
 	{ 0, 1, 0, "remotes" },
 	{ 0, 1, 0, "worktrees" },
 	{ 0, 1, 0, "rr-cache" },