Fixes to audio attenuation jumps and better sample loop script

Yep this was part of what I found/fixed... the code is correct now (I think).... you actually do SumMixes (at least in some sense) for every possible outcome below this line.   The problem was that in some cases where we were clearing shouldAttenuate (for example applying an injector source's volume to the final mix), we were skipping the mix/attentuation pass.