Support showing notes from more than one notes tree

With this patch, you can set notes.displayRef to a glob that points at
your favourite notes refs, e.g.,

[notes]
	displayRef = refs/notes/*

Then git-log and friends will show notes from all trees.

Thanks to Junio C Hamano for lots of feedback, which greatly
influenced the design of the entire series and this commit in
particular.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Acked-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/pretty.c b/pretty.c
index f999485..6ba3da8 100644
--- a/pretty.c
+++ b/pretty.c
@@ -775,7 +775,7 @@
 		}
 		return 0;	/* unknown %g placeholder */
 	case 'N':
-		format_note(NULL, commit->object.sha1, sb,
+		format_display_notes(commit->object.sha1, sb,
 			    git_log_output_encoding ? git_log_output_encoding
 						    : git_commit_encoding, 0);
 		return 1;
@@ -1096,8 +1096,8 @@
 		strbuf_addch(sb, '\n');
 
 	if (context->show_notes)
-		format_note(NULL, commit->object.sha1, sb, encoding,
-			    NOTES_SHOW_HEADER | NOTES_INDENT);
+		format_display_notes(commit->object.sha1, sb, encoding,
+				     NOTES_SHOW_HEADER | NOTES_INDENT);
 
 	free(reencoded);
 }