new ForeignPtr without finalizers

[Alastair Reid]

Ashley:
> How do I create a new ForeignPtr that doesn't have any finalizers?

Malcolm:
> Why would you want to?

addForeignPtrFinalizer lets you add them later.
I'm guessing that Ashley is making heavy use of this ability.

[What we have at the moment is the ability to attach a non-empty list of 
finalizers to an object.  I don't immediately see a use for an empty list but
my experience with various datatypes is that it is usually cleaner to allow 
the empty or zero case and I#'m hoping that Ashley will demonstrate how it is 
useful...]

--
Alastair