[PATCH v2] amstream: Simulate IDirectDrawStreamSampleImpl_Update return values.

[symeonidis at csd.auth.gr]

I've already started working towards a proper implementation of the  
IDirectDraw* interfaces.
However that will probably have to wait until the next release cycle  
(also my Windows installation is currently broken and I have to fix  
that first).
But before that I have a few questions:
1. Is someone else working on implementing any of these functions?
2. Are there any media test files that I can use for the tests?
3. What is the best way to call a method of an interface from inside a  
method of an interface?