rename dirlink to gitlink.

Unify naming of plumbing dirlink/gitlink concept:

git ls-files -z '*.[ch]' |
xargs -0 perl -pi -e 's/dirlink/gitlink/g;' -e 's/DIRLNK/GITLINK/g;'

Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/tree.c b/tree.c
index e4a39aa..a372827 100644
--- a/tree.c
+++ b/tree.c
@@ -157,7 +157,7 @@
 	/* Count how many entries there are.. */
 	init_tree_desc(&desc, item->buffer, item->size);
 	while (tree_entry(&desc, &entry)) {
-		if (S_ISDIRLNK(entry.mode))
+		if (S_ISGITLINK(entry.mode))
 			continue;
 		n_refs++;
 	}
@@ -169,7 +169,7 @@
 	while (tree_entry(&desc, &entry)) {
 		struct object *obj;
 
-		if (S_ISDIRLNK(entry.mode))
+		if (S_ISGITLINK(entry.mode))
 			continue;
 		if (S_ISDIR(entry.mode))
 			obj = &lookup_tree(entry.sha1)->object;