Updated theme functions and menu_block_tree_output() and menu_tree_build() functions. Everything works! (Except the D6 migration path.)

#331933: Help links are displayed if Help module is disabled. Follow-up to add help back to block configure pages.

In Drupal 6, the admin/by-module page won't display Menu block's help link because it doesn't have any non-tab menu links. So to allow Menu block to have some "visibility" in the admin pages, we add a fake-ish page to admin/settings/menu_block that redirects to the "Add menu block" tab.