Add the primitive type Any, and use it for Dynamics

Add the primitive type Any, and use it for Dynamics

GHC's code generator can only enter a closure if it's guaranteed
not to be a function.  In the Dynamic module, we were using the
type (forall a.a) as the type to which the dynamic type was unsafely
cast:
	type Obj = forall a.a

Gut alas this polytype was sometimes instantiated to (), something
like this (it only bit when profiling was enabled)
	let y::() = dyn ()
	in (y `cast` ..) p q
As a result, an ASSERT in ClosureInfo fired (hooray).

I've tided this up by making a new, primitive, lifted type Any, and
arranging that Dynamic uses Any, thus:
	type Obj = ANy

While I was at it, I also arranged that when the type checker instantiates
un-constrained type variables, it now instantiates them to Any, not ()
	e.g.  length Any []

[There remains a Horrible Hack when we want Any-like things at arbitrary
kinds.  This essentially never happens, but see comments with
TysPrim.mkAnyPrimTyCon.]

Anyway, this fixes Trac #905