flac muxer: add option to disable writing the global header

The global header is not explicitly required for playback, and
omitting it allows for simple concatenation.
lavfi: add framepack filter
fate: add framepack filter test
avfilter: add documentation for needs_writable
avfilter: add needs_writable field to the internal AVFilterPad structure
avfilter: fix leaks on error in ff_filter_frame
avutil: do not use avcodec header in frame.h
Merge commit 'aa69cbc9e08281db6ecb98a2c8b4f60e8b12e558'

* commit 'aa69cbc9e08281db6ecb98a2c8b4f60e8b12e558':
  flac muxer: add option to disable writing the global header

Conflicts:
	libavformat/version.h

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'a7d0e7ead95e584c4866617f046b2493066975c6'

* commit 'a7d0e7ead95e584c4866617f046b2493066975c6':
  lavfi: add framepack filter

Conflicts:
	Changelog
	doc/filters.texi
	libavfilter/allfilters.c
	libavfilter/version.h

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '11d704dc94c029058ac366f85951f6728638fb9c'

* commit '11d704dc94c029058ac366f85951f6728638fb9c':
  fate: add framepack filter test

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'd44bd7fb27d4121512eae0ffce5e48bac25e82dc'

* commit 'd44bd7fb27d4121512eae0ffce5e48bac25e82dc':
  avfilter: add documentation for needs_writable

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '5655732c77f2df9c1dfbddc30cd4844390a6921f'

* commit '5655732c77f2df9c1dfbddc30cd4844390a6921f':
  avfilter: add needs_writable field to the internal AVFilterPad structure

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'abb5e37f64c48bba8bd0fde2bada0f7544defa24'

* commit 'abb5e37f64c48bba8bd0fde2bada0f7544defa24':
  avfilter: fix leaks on error in ff_filter_frame

Conflicts:
	libavfilter/avfilter.c

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

* qatar/master:
  avutil: do not use avcodec header in frame.h

Merged-by: Michael Niedermayer <michaelni@gmx.at>
fate: fix MSS2 tests on big endian

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