threads: Check w32threads dependencies at the configure stage

Also add warning comment about threading implementations without matching
atomics implementation to the atomics fallback implementation.
doc: Sort the muxer documentation

Keep the sections alphabetically sorted.
doc: Name the MOV muxer as it should be called

The section name is the muxer, not the format.
hevc: Mention the missing SPS in the error message
Add decklink_enc.h to SKIPHEADERS.

Fixes make checkheaders without decklink headers.
avcodec/huffyuv: simplify allocation of temporaries

This also fixes a null pointer dereference with rgb and plane prediction

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '874c751cc5b99cd68932e21c2c3a0d21134207e0'

* commit '874c751cc5b99cd68932e21c2c3a0d21134207e0':
  threads: Check w32threads dependencies at the configure stage

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'a7b3216cbdc7796a9d14cd22a863fae3556098ba'

* commit 'a7b3216cbdc7796a9d14cd22a863fae3556098ba':
  doc: Sort the muxer documentation

Conflicts:
	doc/muxers.texi

No change as ours was already sorted

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '93632a70f9ac2cb2ebf0e69d21fdfaae68ff02fd'

* commit '93632a70f9ac2cb2ebf0e69d21fdfaae68ff02fd':
  doc: Name the MOV muxer as it should be called

Conflicts:
	doc/muxers.texi

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '175e5063320f585118a5461f15dbacf2ce17e97d'

* commit '175e5063320f585118a5461f15dbacf2ce17e97d':
  hevc: Mention the missing SPS in the error message

Merged-by: Michael Niedermayer <michaelni@gmx.at>