From my experience, I think include uses the relative path of WHERE it is called. so if you have the following:
php1.php
<?php
include "includes/php2.php;
?>
php2.php
<?php
include "php3.php";
?>
It will NOT look php3.php inside includes/ , but instead will look inside the folder of php1.php. So whatever you include in mysql_handler.php may need to use the path of the first php file in your stated directory "include/phpscripts"
Again, I'm not sure if it exactly works out that way.
Good luck