Audit against CFB

[waveform80]

Now that MS have managed to come up with a well written spec (considerably better than the awful AAF one) we should go through and audit the codebase against it. I've spotted several little bits to deal with already (checking sector size instead of DLL version when looking at the high 32-bits of entities, transaction signature is permitted to be non-zero, CLSID can be non-zero for storages but not streams, etc. etc.)

This can wait for now, but it should definitely be done before 1.0.