pvr250 - can't select input

[Dom F]

Thanks to Mark for pointing out my missing "-g" geometry selection and 
that S-video might not be supported in PVR250.

After some testing I found that composite works OK but S-video does not. 
I find composite input better than tuner but I might have a quick go at 
spotting the S-video enabling code and retrofitting it back to pvr250.

I'm not entirely sure if multimedia/pvrxxx is supposed to support pvr250 
(and all other pvr models) or just pvr150/pvr500? Should the pvr250 port 
be deprecated/removed in favour of unified pvrxxx if this is the case?
I've built the pvrxxx port before so another thing I can test is whether 
pvrxxx supports pvr250, specifically the S-video input.

Dominic