function check_user($username, $password) {
	global $connection, $DB_usertable;

	$query ="SELECT * FROM $DB_usertable WHERE username='$username' and password=MD5('$password')";
	$result = mysqli_query($connection, $query) or die("$query - ".mysqli_error($connection));
	$user=mysqli_fetch_assoc($result);
	if (!empty($user)) {
		return $user;
	}	else {
		return false;
	}
}