Referring to missing types does not generate an error

[j14159]

module x

type a = int | b

This doesn't generate an error about an undefined type b and it should.

Thanks to @danabr for pointing this out in IRC

[danabr]

Referring to an unknown type variable should also be an error. Currently, the compiler let's this through:

type baz 'a = Baz 'c

let woot Baz _ = :ok

Should we squash that one at the same time, or would you prefer a separate issue?

[j14159]

Seems like part of the same issue to me, thanks for adding this!