Let --decorate show HEAD position

'git log --graph --oneline --decorate --all' is a useful way to get a
general overview of the repository state, similar to 'gitk --all'.
Let it indicate the position of HEAD by loading that ref too, so that
the --decorate code can see it.
Signed-off-by: NThomas Rast <trast@student.ethz.ch>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

log-tree.c

@@ -43,6 +43,7 @@ void load_ref_decorations(int flags)
 	if (!loaded) {
 		loaded = 1;
 		for_each_ref(add_ref_decoration, &flags);
+		head_ref(add_ref_decoration, &flags);
 	}
 }
 

t/t4013/diff.log_--decorate=full_--all

 $ git log --decorate=full --all
-commit 59d314ad6f356dd08601a4cd5e530381da3e3c64 (refs/heads/master)
+commit 59d314ad6f356dd08601a4cd5e530381da3e3c64 (HEAD, refs/heads/master)
 Merge: 9a6d494 c7a2ab9
 Author: A U Thor <author@example.com>
 Date:   Mon Jun 26 00:04:00 2006 +0000

t/t4013/diff.log_--decorate_--all

 $ git log --decorate --all
-commit 59d314ad6f356dd08601a4cd5e530381da3e3c64 (master)
+commit 59d314ad6f356dd08601a4cd5e530381da3e3c64 (HEAD, master)
 Merge: 9a6d494 c7a2ab9
 Author: A U Thor <author@example.com>
 Date:   Mon Jun 26 00:04:00 2006 +0000