[mythtv] zoom for non-4:3/16:9

[Preston Crow]

I have a 16:9 TV, so when watching a standard-definition letterboxed
show, I hit 'w' to zoom in and fill the screen.  Great feature!

I've noticed that some shows are in some in-between format, where they
have smaller black bars at the top and bottom.  I don't know the exact
aspect ratio, but it seems to be common on BBC America.  Having the zoom
feature for this aspect would be really nice.  (Is there a name for that
format?)

Oh, and a configuration setting to disable zoom modes that I don't use
would be nice.


I can write a patch if it's likely to be accepted and none of the other
developers wants to preempt me.

--PC