mplex as well), due to inconsistencies in how the mpeg_aspect_ratio
and mpeg_framerate arrays were constructed/used.
I restructured the code a bit to clean up the interface, so that I
could fix the bugs (without going cross-eyed) and to make it less
susceptible to such errors in the future.
Andrew: I do indeed step most gingerly when I walk into your code!
I'm not married to this revised interface in mpegconsts.[ch],
but it's a little cleaner and it fixes some plain old bugs.
