Improve display of builtin types by the toplevel

[samsa1]

Currently the toplevel uses type information to know how to display types such as lists.
However this works only if the type is exactly the builtin types and not an alias.

Thus the some examples are not displayed as nicely as they could :

# let f (l : 'a list) : 'a List.t = l
  ;;
val f : 'a list -> 'a List.t = <fun>
# f [3; 2];;
- : int List.t = List.(::) (3, [2])

The change proposed by this PR is to check if a type correspond to a builtin type through aliases to detect more occurrences of builtin types.

[samsa1]

Sorry I had a problem of mixed commits with another PR that is already merged. I'll try to clean up the diffs

[samsa1]

Ok, I managed to clean up the code, this should help reviewing

[Octachron]

This is a clear improvement with a minimal code complexity cost. Even if not all possible cases are not handled, the more confusing one should be covered. In particular, using

open List

doesn't break the toplevel list printer anymore.

Thus I think it is better to merge this PR. Thanks!