Load all the important user information.
What it does:
- sets up the $user_info array
- assigns $user_info['query_wanna_see_board'] for what boards the user can see.
- first checks for cookie or integration validation.
- uses the current session if no integration function or cookie is found.
- checks password length, if member is activated and the login span isn't over.
- if validation fails for the user, $id_member is set to 0.
- updates the last visit time when needed.