In `BP_Component::setup_admin_bar()` filter the passed `$wp_admin_nav` parameter to allow plugins to modify menu contents before they are added to the `$wp_admin_bar` global. This filter is necessary because `WP_Admin_Bar` does not have filters in place to allow easy modification of menu items without already knowing their unique identifiers.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7410 cdf35c40-ae34-48e0-9cc9-0c9da1808c22