Potentially fix segfaults on frontend startup

In nvctrl-util's GetNvidiaRates():
Initialise buf values to NULL, reduce it's size from 256 to 8 since
we're only interested in the first 8 tokens and actually check that we
parsed all 8 from the string before proceeding to use them.

While here change logging from VB_PLAYBACK to VB_GUI which makes more sense.

This may fix some frontend startup segfaults experienced by some
people since we ended up using an area of uninitialised memory in
strtol.

Coverity 746855
(cherry picked from commit 516719ad7e750a258bd2f72f79eae099f79d303b)
Pull in fix for out-of-bounds array write in xine_demux_sputext.cpp from upstream. Coverity 746831
(cherry picked from commit 70309164e52c24a69cc151d3b37036e68e45f096)
Fix fence post error in 516719a
(cherry picked from commit ec3a978eec841652993147940472c9a059c2c14b)
MythSystem: Fix copy/paste in [8532584f]
(cherry picked from commit 1d3ffebc9b81114b1d212dc9b59386fd4717d747)
Mostly revert 788bc510.  It's not needed and created a new bug.

That change was intended to fix a deadlock.  In reality, it only
worked around the deadlock and added a race condition that could cause
delayed handling of reschedule requests.  It was a series of later
changes that actually fixed the deadlocks, so this fix can be fixed by
reverting it.

(cherry picked from commit aafa07e9e314793990e7f58f30bfb6199a430978)
Don't skip over recordings that are still tuning.

Fix a bug where the scheduler sometimes skips over recordings in the
rsTuning state.  This doesn't matter normally as the recording usually
transitiions to the rsRecording state quickly.  When there is a tuning
problem, however, this bug defeats the tuning timeout check in the
scheduler and the recording gets stuck in the tuning state.  This fix
makes sure the tuning check is always done.

(cherry picked from commit f455e491239cc128200db85c90dcab7ea15044c3)