Merge: type works: handle implicitly fixed formal parameters

~~~
class G[E: Int]
   # Here, since Int cannot have a subclass, then E == Int (implicitly fixed)
end
~~~

This series enhance the type system to understand this case, and give the user a warning when bounding formal parameter with final classes.

Pull-Request: #618
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>

diff --cc src/modelize_class.nit
Simple merge

diff --cc src/typing.nit
Simple merge