Use blob_, commit_, tag_, and tree_type throughout.

This replaces occurences of "blob", "commit", "tag", and "tree",
where they're really used as type specifiers, which we already
have defined global constants for.

Signed-off-by: Peter Eriksen <s022018@student.dtu.dk>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/ls-tree.c b/ls-tree.c
index 26258c3..e4ef200 100644
--- a/ls-tree.c
+++ b/ls-tree.c
@@ -56,7 +56,7 @@
 		     const char *pathname, unsigned mode, int stage)
 {
 	int retval = 0;
-	const char *type = "blob";
+	const char *type = blob_type;
 
 	if (S_ISDIR(mode)) {
 		if (show_recursive(base, baselen, pathname)) {
@@ -64,7 +64,7 @@
 			if (!(ls_options & LS_SHOW_TREES))
 				return retval;
 		}
-		type = "tree";
+		type = tree_type;
 	}
 	else if (ls_options & LS_TREE_ONLY)
 		return 0;