Fix #2771: pre-check kinds at Typer

[odersky]

We normally do kind checking during PostTyper, together with bounds checking.
However, this is not early enough, as #2771 shows. The problem is that we can
use ill-kinded code to construct self applications of types, which leads to general
unhappiness in the typer. Prevent that by checking the outline of kinds of types
as soon as we create them.

[smarter]

While this PR helps avoid some absurd applications, I don't think it solves the fundamental issue where a type can be seen as having multiple kinds because of bad bounds, here's a slightly modified test case that causes a stackoverflow while beta-reducing:

trait A { type L[X[_]] }
trait B { type L }
trait C { type M <: A }
trait D { type M >: B }

object Test {
  def test(x: C with D): Unit = {
    def f(y: x.M)(z: y.L[y.L]) = z
    f(new B { type L[F[_[_]]] = F[F] })(1)
  }
}

[smarter]

LGTM because I can't break it anymore :) (maybe @sstucki can?). It'd be nice to give more detailed error messages (instead of just saying "has wrong kind", say what the actual and expected kinds are), but we can address that separately.

[sstucki]

Found a way to break the fixed version, though the error is different. See #2887.