Hadrian should warn when multiple flavours have same name

A flavour like this

userDefaultFlavour :: String
userDefaultFlavour = "default"

userFlavour :: Flavour
userFlavour = Flavour { name = userDefaultFlavour,  ... }

is hard to use (if not impossible) because (I think) by default there's another flavour with the name "default" already defined (in Settings.hadrianFlavours) so when I ask hadrian to use the "default" flavour the other one is used instead of mine.

I think Hadrian should be warning the user when multiple flavours have the same name as some of those flavours will be unusable by the user.