Thanks, bgupta16: the sentence:
I hope you have copied the "mysql.php" and "MMHTTPDB.php" files from "C:\Users\username\AppData\Roaming\Adobe\Dreamweaver CC\locale\Configuration\Connections\Scripts\PHP_MySQL\_mmDBScripts" to "C:\xampp\htdocs\phptest\_mmServerScripts"
did the trick!
So we have to manually copy these file now? In previous DW versions they were copied automatically...