Ensure compatibility for upgrade from 2.x

Frankly, I don’t think anyone should use this module for new PHP code, but should instead be creating a hook in a module but, as this module is handy for people who are upgrading, it would seem most helpful to provide compatibility with existing WebForm 2.x PHP scripts.

With this in mind, I discovered that the 3.x version does not make the $user variable global. In my mind, whether or not 2.x should have made it global is secondary to the issue of backward compatibility.

This patch corrects this incompatibility regression.