This patch uses local URLs in parameters because it is more compatible
with various security hacks. Session key is not added automatically to
return url for safety reasons - we do not want to execute some random
action again. POST pages are now returned to course page too.
This patch introduces two new blocks global_navigation_tree and settings_navigation_tree
both of which have been designed to make full use of the new navigation objects available through
the $PAGE object.
Bulk of this code is within lib/navigationlib.php
