ADMX support definitions can reference other support definitions

I just did some science on the "Limit the maximum network bandwidth for BITS background transfers" policy setting to see if the real Group Policy Editor actually resolves references to support definitions from other support definitions. I filtered the policies for ones that support Windows XP SP2 (which is only attached to that policy setting via a referenced support definition), and that one showed up. Therefore, the Group Policy Editor can handle cases like these.

I'll have to change Policy Plus's AdmxBundle class to try to fold referenced definitions into containing ones. Alternatively, I could adjust the support definition class to be able to hold a list of mentioned definitions, then the component that actually cares about support would be responsible for avoiding infinite loops or stack overflows.