Menu system regression: Local tasks no longer passing through theme('menu_item_link')

Previously, local tasks (Tabs) passed through theme('menu_item_link'). Currently they go directly through l(). It is necessary for themes to be able to theme the link in order to do pretty tabs, as it often requires putting markup inside the <a> tag in order to achieve the proper look. This worked in Drupal 5.

This patch restores this functionality.