BigInt and other j.l.Numbers are considered AnyVals instead of AnyRefs with Typeable

[sjrd]

The following test case fails:

    val n: Any = BigInt(23)
    val cn = n.cast[AnyRef]
    assertTrue(cn.isDefined)

    val cn2 = n.cast[AnyVal]
    assertTrue(cn2.isEmpty)

This is because Typeable.isValClass uses classOf[j.l.Number].isAssignableFrom(clazz) instead of explicitly listing the 6 boxed number classes:

shapeless/core/src/main/scala/shapeless/typeable.scala

Lines 77 to 81 in ded1d04

	def isValClass[T](clazz: Class[T]) =
	(classOf[jl.Number] isAssignableFrom clazz) ||
	clazz == classOf[jl.Boolean] ||
	clazz == classOf[jl.Character] ||
	clazz == classOf[runtime.BoxedUnit]

java.math.BigInteger, scala.math.BigInt and their decimal counterparts are examples of AnyRef types that are subclasses of java.lang.Number.