Work around the runtime type issues in Scala.

[vivri]

From the running spec:

    // First, we define the precise types that make up our domain/universe/ontology
    object PersonOntology {
      // `Adjective[T]` is the building block of our type algebra
      // Try to make them as atomic as possible
      case object DbId                extends Adjective[Int]    ((id)=> 0 <= id && id < 2000000)
      case object NameSequence        extends Adjective[String] (_.matches("^[A-Z][a-zA-Z]{1,31}$"))
      case object DisallowedSequences extends Adjective[String] (_.toLowerCase.contains("fbomb"))
      case object ScottishLastName    extends Adjective[String] (_ startsWith "Mc")
      case object JewishLastName      extends Adjective[String] (_ endsWith "berg")

      // We use boolean algebra to combine base adjectives into more nuanced adjectives
      val LegalName = NameSequence & ~DisallowedSequences // `~X` negates `X`
      val FirstName = LegalName
      val SomeHeritageLastName = LegalName & (ScottishLastName <+> JewishLastName) // `<+>` stands for Xor, ⊕ is the math notation
    }

    // < ... Irrelevant things go here > 

    // Trying to precisely type the Includes/Excludes exposes a
    // little bit of clunkiness in the path-dependent types of `val`s
    validPerson shouldBe Right(
      Person(
        Includes(DbId,123), // this works great because DbId is a type, not a `val`
        Includes(FirstName, "Bilbo").asInstanceOf[FirstName.^], // ouch!
        Includes(SomeHeritageLastName, "McBeggins").asInstanceOf[SomeHeritageLastName.^])) // one more ouch.

This is very clunky, and detracts from both the usability and safety of using the library.

I believe it is caused by the fact that Scala treats static and dynamic type declarations differently, with the dynamically-declared type being a second-rate citizen.

We should create a mechanism whereby this wart is either hidden behind some library interface, or avoided altogether.