Adds alsa09 ao output support to ao.c, mpg321.h, and
It Works For Me, but if you want it to work for you
then you'll need a fixed libao alsa09 output driver.
I've submitted a patch for that to bugs.xiph.org, but
haven't heard back from anyone about it. I'm not quite
sure who the project maintainer is, so it couild be awhile.