core: INCOMPATIBLE CHANGE: Name repo files with their type (e.g. .dirmeta)

This makes inspection easier.  Internally the code gets simpler because
metadata and files are more unified; there is just one object type.

src/ostree/ot-builtin-checksum.c

@@ -79,7 +79,7 @@ ostree_builtin_checksum (int argc, char **argv, const char *repo_path, GError **
 
   data.loop = g_main_loop_new (NULL, FALSE);
   data.error = error;
-  ostree_checksum_file_async (f, OSTREE_OBJECT_TYPE_FILE, G_PRIORITY_DEFAULT, NULL, on_checksum_received, &data);
+  ostree_checksum_file_async (f, OSTREE_OBJECT_TYPE_RAW_FILE, G_PRIORITY_DEFAULT, NULL, on_checksum_received, &data);
   
   g_main_loop_run (data.loop);