[mythtv] Automatic deletion

[Jim Paris]

> "Auto-Delete Order (delete in this order)"
> 
> 	* OFF
> 	* Oldest
> 	* Oldest Unwatched
> 	* Lowest Rating

Somewhat related: there should also be a configurable option so that
if Myth can't or was told not to delete any more stuff, but the
available space still falls below a certain percentage, it should just
stop trying to record.  Several times now I've spent several minutes
figuring out why my load average kept shooting up to 4-5 and new shows
wouldn't record only to discover that I had 0 bytes free...

Yeah, I know, submit patch etc etc.  Will do if I get time to
actually do it :)

-jim