actually, I found that post through search. After backing up to the beginning, I realized that it is a add-on. So now I'm attempting to install the add-on in beta 5. having issues with that too, but let me try a few things and I'll get back to ya.
* Determines if a user is a member of a particular user group
* @param array $user
* @param integer $userGroupId
* @param boolean Also check secondary groups
* @return boolean
public function isMemberOfUserGroup(array $user, $userGroupId, $includeSecondaryGroups = true)