WENO5Z-AOAH behavior: alpha > 1.0

[AstroBarker]

When tracking down some other behavior I noticed weirdness in our WENO5-Z implementation: the alpha_lin value (sigma in the paper) can transiently become slightly larger than 1.0. This should not be happening. I'm not sure yet what the implications are (there are no obvious signs of ill behavior when this happens). If I recall correctly, the shock tube is sufficient to trigger this. The relevant variable is here.