- Removed register_globals related code and "!" can be used as $_SESSION key name.
- Session is made to manage session status correctly and prevents invalid operations.
Only inappropriate codes are affected by this change. If you have problems with this,
it means you have problem in your code.
- Functions are made to set or return correct session status. session_start(), session_status(), session_regenerate_id()
- Functions are made to return bool from null. These functions have void parameter