fix for broken flyouts when Theme Developer is running

When the Theme Developer module is enabled, the flyout menus cease working. Based on interaction with tha_sun on IRC, I implemented his recommended fix, which seems to work nicely.

Two changes were introduced where:

$output .= theme('admin_menu_item', $link, $data['link']['has_children'], admin_menu_tree_output($data['below']), $data['link']['in_active_trail'], $extra_class);

was converted to

$output .= theme_admin_menu_item($link, $data['link']['has_children'], admin_menu_tree_output($data['below']), $data['link']['in_active_trail'], $extra_class);

and

$output .= theme('admin_menu_item', $link, $data['link']['has_children'], '', $data['link']['in_active_trail'], $extra_class);

was converted to

$output .= theme_admin_menu_item($link, $data['link']['has_children'], '', $data['link']['in_active_trail'], $extra_class);