[mythtvnz] Use different tuner for adjacent recordings

[Noel & Di]

>
> I do have 4 recordings going at
> once probably twice a week or so, but I have never had 4 all with
> back-to-back recordings, so I can not say for sure that a single disk
> would not cope.
I have 2x2 programs record back to back every weeknight, and only have 
issues if we watch a fifth previously recorded program. 
I have set my  recording rule to start & finish 5 mins early, & this is 
the default for any new recordings. 
The only issue I need to be careful of is to make sure SBS recordings 
have a lower priority than any freeview channels (SBS is vertical 
polarization so effectively eliminates  further use of horizontal 
multiplexes for the duration of the recording on that tuner), that & the 
pesky AU daylight saving times!
Noel