System module's "listing" pages (and blocks) should use menu_build_tree()

Spin-off from #519046: Clean up toolbar menu code and #296693: Restrict access to empty top level administration pages:

System module as well as Toolbar module as well as a couple of contrib modules require a menu system function to build a menu tree that starts from a given menu link and optionally ends at a specified level.

menu_tree_all_data() already takes an optional $max_depth parameter, but the $link parameter that can be passed in only allows to specify something along the lines of an active trail for the requested menu tree.

By introducing this, we can eliminate approx. 300 lines of totally awkward code from system.module, system.admin.inc, and toolbar.module - AND - most likely improve performance.

http://api.drupal.org/api/function/system_admin_menu_block_page/7
http://api.drupal.org/api/function/system_admin_config_page/7
http://api.drupal.org/api/function/system_admin_menu_block/7

Excerpt from Toolbar module:

+++ modules/toolbar/toolbar.module	6 Oct 2009 17:41:17 -0000
@@ -120,14 +120,12 @@ function toolbar_get_menu_tree() {
-    $tree = menu_tree_all_data('management', $admin_link);
+    // @todo Use a function like book_menu_subtree_data().
+    $tree = menu_tree_all_data('management', $admin_link, $admin_link['depth'] + 1);
     // The tree will be a sub-tree with the admin link as a single root item.
+    // @todo It is wrong to assume it's the last.
     $admin_link = array_pop($tree);
     $tree = $admin_link['below'] ? $admin_link['below'] : array();

So what we need here is a simple menu_subtree_data() function, which may even already exist, ready for rumble, in http://drupal.org/project/menu_block