Change $callbacks to $items in hook_menu_alter()

Changed references in the only hook_menu_alter() reference in core.

Unit tests didn't appear to have any references.

There are a few more replacements in menu.inc that we should do as well for consistency:

./includes/menu.inc:1810:      $callbacks = array();
./includes/menu.inc:1817:          $callbacks = array_merge($callbacks, $router_items);
./includes/menu.inc:1821:      drupal_alter('menu', $callbacks);
./includes/menu.inc:1822:      $menu = _menu_router_build($callbacks);
./includes/menu.inc:2410:function _menu_router_build($callbacks) {
./includes/menu.inc:2414:  foreach ($callbacks as $path => $item) {
./modules/menu/menu.api.php:91: * in by reference. Each element of the $callbacks array is one item returned
./modules/menu/menu.api.php:95: * @param $callbacks
./modules/menu/menu.api.php:100:function hook_menu_alter(&$callbacks) {
./modules/menu/menu.api.php:102:  $callbacks['node/add']['access callback'] = FALSE;

Fixed the other references as pointed out by Dave Reid.

$items is very ambigious and unclear. We should do the opposite - hook_menu() implementations should use $callbacks, not $items.

Does not apply directly to docs/hooks/core.php in 6.x. Needs backport.

I went ahead and committed the change to docs/hooks/core.php since any CVS user has commit access to that project.
http://drupal.org/cvs?commit=172153

This is now fixed! Thanks everyone!