pthread: Rename thread_init to avoid symbol collision

The AIX threads library exposes a function with the same name.

Signed-off-by: Martin Storsjö <martin@martin.st>
fmtconvert: Explicitly use int32_t instead of int

Signed-off-by: Martin Storsjö <martin@martin.st>
Merge commit '50612484e058e8b241f0528584d64d9d2ccebf12'

* commit '50612484e058e8b241f0528584d64d9d2ccebf12':
  pthread: Rename thread_init to avoid symbol collision

Conflicts:
	libavcodec/pthread.c
	libavfilter/pthread.c

See: 674d8a9629609a17fd6916164556cb012d6e6a1c
Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  fmtconvert: Explicitly use int32_t instead of int

Conflicts:
	libavcodec/ac3dec.c
	libavcodec/fmtconvert.c
	libavcodec/fmtconvert.h

See: f49564c6075935443323abf4571a62205e7b3c59
Merged-by: Michael Niedermayer <michaelni@gmx.at>
lavf/matroskaenc: Check for valid metadata before creating tags

Tags must have at least one SimpleTag element to be spec conformant.
Updated lavf-mkv and seek-lavf-mkv FATE references as the tests were affected by
this.

Fixes ticket #2785

Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>