public interface FacadeTextBuffer
A text buffer that delegates its calls to a wrapped 'real' buffer.
The purpose of the facade is that it is referenced via a weak reference.
The weak reference is periodically checked to see if it has been nulled out
(i.e. No one else refers to it) and auto closes the node.
So it is important that all external references to the text buffer are via this
facade, otherwise the auto close mecahnism won't work and we'll leak lots of memory.