Previously LUs could be failed by pre-hooks, and post-hooks just had effects by
themselves. This patch allows a LU to define the HooksCallBack function if it
wants to know about its hooks' results and alter its results in response.

The ChainOpCode execution path contains some commented out hooks code, which
this patch modifies to run the HooksCallBack function, so this is not forgot if
it ever gets uncommented out.

Reviewed-by: iustinp