[pvr.tvh] - fixed mistake on fileSeek return, that cause rev. seek to fail
[pvr.tvh] - added extra debug while hunting down timeshift issues
[pvr.tvh] - some minor improvements to initial data download handling
[pvr.tvh] - fix timeshift (and other) problems? By increasing packet buffer.

I (and others) had completely failed to notice that the default buffer size
for the SyncedBuffer object that pvr.{hts,tvh} was using is ridiculously small
and thus could result in lost data (worse there was no error output - doh).

I have increased to unlimited length, its implicitly bounded by other things
and there is little point bounding it. If it were to fill indefinitely then
something would have to be seriously wrong and the system would probably
eventually crash for other reasons!

This appears to fix timeshift issues, I wonder whether it will fix other things
as well!