[FIX] Revert r45969 ([FIX] User not in registered group when using CAS)
This commit broke creating new users as the admin user would end up with the userid of the new user, and thus lose admin rights.
Sorry, cannot test for CAS now, but please find another way of doing this. Setting the session value of the current user's id to effectively a random number can't be right.

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/11.x@46388 b456876b-0849-0410-b77d-98878d47e9d5