References to variant cases: do not splice the type name in. 

If I have : 
```ocaml
module Bla : sig
  type ha = Alpha | Beta
end

Use {!Bla.Alpha} to say alpha.
```
The latter line gets rendered as:
```
Use Bla.ha.Alpha to say alpha.
```
This should simply be `Bla.Alpha`, I don't think `odoc` should invent OCaml syntax that doesn't exist.


