Add access check error message, Allow forged internal requests

By allowing forged internal requests, you can switch to fbf at a
late-stage fuseaction (for instance when choosing and rendering the
layout, after the building blocks have been generated) This allowed me
to revert fusebox and remove the dirty layout hacks that I'd used to get
it to run 3 separate layouts. (do tags are usually static and can't be
modified at runtime!)