Updates for Virgin Media TiVo Review and PVR Comparison Document

The review I did for TiVo has been updated, mainly with a 'for' (series links can find alternative broadcasts of a programme on the same channel if the original recording of that programme couldn't be completed), and, an 'against' (no access to live PPV events content until a future software update).

The PVR Comparison Document has also been updated, now that the 500Gb version of TiVo is available to existing customers.