Make UnitCreatureType work like UnitClass

[elnlc]

UnitClass is great for language neutral AddOns as it returns both the localized name and the internal code name. You can work consistently with the internal code name to make your AddOn work on all localized versions of WoW.

Unfortunately, UnitCreatureType only returns the localized name. It would be nice to make it return the internal name aswell. This would avoid cross language compatibility problems.