Rescale 1088-row videos to avoid showing trailing garbage.

Refs #11358.  1080i videos may present themselves as 1088 rows
(divisible by 16).  The HD-PVR in particular may contain garbage in
those last rows.  Specifically, the last two rows may form an annoying
green line.  We add a scaling pass to shift the bottom 4 rows (4 to be
on the safe side) off the bottom of the display area.
(cherry picked from commit 9d9de7b75d5354c9130526311a0c74d7172ebe6d)
Fix issues which sometimes prevente scheduling around live TV.

Backport of SHA1:b05ecd46 to fixes/0.26.

There are some cases where we don't attempt to schedule around live
TV.  This change cleans up the logic which determines when to do that
and fixes some of the bugs found in the process.

NB: the case where a user enters live TV immediately before a
recording is scheduled to start is still not handled gracefully.
Fixing that is a lot tougher and will likely mean involving the
scheduler in choosing which input to use for live TV.

Refs #11207
Revert "Temporary fix for #11159: Fix playback of HD-PVR recording"

This reverts commit 3c8d88ac55c2b2c1bc652076d7824529254829a4.

It breaks BBC-HD playback consistently.