bug: formal types in class refinements can be named as real types

[Morriar]

Exemple:

redef class Array[Char]
    fun foo(c: Char) do 
        print c.is_alpha
    end
end

When compiling this code the compiler throws the error:
Error: Method 'is_alpha' doesn't exists in Array#0.
print c.is_alpha

Here the redef of Array with the formal type name Char must be rejected by the compiler because a type with the name Char already exists.

Assigned to @Morriar