Ensure drivers loaded before failing

so that deprecated are known
PLAT-132

@e0d plz test: this should fix your problem
any(@doctoryes @mulby @cpennington) plz review

Did red, green TDD
Didn't actually unload the classes; so, 'deprecated_fallback' is still set. Unsetting it doesn't work b/c it only gets set when the module's loaded and the module's already loaded.