Effect Processor Improvement

This adds an improvement to both the legacy and new Effect content processor.  Previously if you had and include in your FX file like so:

```
#include "common_stuff.fxh"
```

And you altered the content of the `common_stuff.fxh` file the pipeline would not rebuild any effects.   This was because it doesn't register the dependency during the build.  This was also a problem in stock MS XNA.

This changes has us return the found `#include`s to the processor and register them as build dependencies.  This means when any of these files are changed all referencing FX files are rebuilt as one would expect.

This has been fully tested.