An ExternalAddress is an opaque handle to objects outside Smalltalk memory (e.g., a pointer).

	converting
	asInteger fromInteger:

	initialize-release
	beNull free

	printing
	printOn:

	private
	asByteArrayPointer

	instance creation
	allocate: new new:

	accessing	top
	byteAt: Go through a different primitive since the receiver describes data in the outside world
	byteAt:put: Go through a different primitive since the receiver describes data in the outside world
	isExternalAddress Return true if the receiver describes an object in the outside world

	converting	top
	asInteger convert address to integer
	fromInteger: set my handle to point at address.

	initialize-release	top
	beNull Make the receiver a NULL pointer
	free Primitive. Free the object pointed to on the external heap. Dangerous - may break your system if the receiver hasn't been allocated by ExternalAddress class>>allocate:. No checks are done.

	printing	top
	printOn: print this as a hex address ('@ 16rFFFFFFFF') to distinguish it from ByteArrays

	private	top
	asByteArrayPointer Return a ByteArray describing a pointer to the contents of the receiver.

	class initialization	top
	startUp: This message is sent to registered classes when the system is coming up.

	instance creation	top
	allocate: Primitive. Allocate an object on the external heap.
	new External addresses are always 4 bytes long
	new: You better don't try this...