[FIX] Do not show the buttons "Go back" and "Return to home page" if the error occurs on the homepage.
Cleans up the look when the user has no permissions. 
The buttons are displayed on all other pages.

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/12.x@49578 b456876b-0849-0410-b77d-98878d47e9d5