[ticket/11997] Undo changes to phpbb_own_realpath()

PHPBB3-11997
[ticket/11997] Add method for controller redirect URLs to path helper

This method will allow us to get proper redirect URLs for controllers.

PHPBB3-11997
[ticket/11997] Use get_controller_redirect_url() in redirect() function

This method of path_helper will now be used instead of the previous hack
of the phpbb_own_realpath() function.

PHPBB3-11997
[ticket/11997] Fix tests for path_helper's get_controller_redirect_url()

PHPBB3-11997