In need for CommonOriginalType

["Nordlöw" via Digitalmars-d-learn]

In order to make

https://github.com/nordlow/justd/blob/master/enums.d

more type-safe (restrict type arguments to EnumUnion) I need a 
type trait, say,

CommonOriginalType(E...)

Do I have to use recursion (like in CommonType) to implement this 
or is there a better way?

See also:
http://forum.dlang.org/thread/bjburcdtcejohtpmqmay@forum.dlang.org?page=2#post-lveiwblfoommtjninxki:40forum.dlang.org