avformat/utils: dont count attached pics toward the probesize

Such pics behave more like headers which we also dont count.
Fixes Ticket3146

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit a8dec360c5db15e8da4b44ff3c0f02a6c57e8ac0)
build: avoid stdin stall with GNU AS probing.

a758c5e added probing for various tools, such as AS. Unfortunately, GNU
AS is reading stdin with -v, and thus configure is stalled with
configure arguments such as --as=as.

Fixes Ticket #1898.
(cherry picked from commit dbb41f93c16cbc65a899a75723c95da51c851cd5)
avformat/image2: allow muxing gif files.

Fixes Ticket #2936.
(cherry picked from commit f70db22999d713da3306bf29ec763d670b9bf1ea)

Conflicts:
	libavformat/img2enc.c
lavd/lavfi: support unknown channel layouts.
(cherry picked from commit 863fb11f63f7f60feec390f3c54dd13606e07d05)
lavfi/avfiltergraph: suggest a solution when format selection fails.

Format selection can fail if unknown channel layouts are used
with filters that do not support it.
(cherry picked from commit f775eb3fb4c7b716107355e428e40cb63f71ee7a)
lavfi/avfiltergraph: do not reduce incompatible lists.

A list of "all channel layouts" but not "all channel counts"
can not be reduced to a single unknown channel count.
(cherry picked from commit d300f5f6f570659e4b58567b35c9e8600c9f2956)
lavfi: parsing helper for unknown channel layouts.

Make ff_parse_channel_layout() accept unknown layouts too.
(cherry picked from commit 6e2473edfda26a556c615ebc04d8aeba800bef7e)
lswr: fix assert failure on unknown layouts.
(cherry picked from commit 4a640a6ac89099bfb02d6d3d3ada04e321a37476)
lavfi/af_pan: support unknown layouts on output.
(cherry picked from commit 4e9adc9b7363cc336e3d47c98455e1508902fd29)
lavfi/af_pan: support unknown layouts on input.

Fix trac ticket #2899.
(cherry picked from commit 7b0a587393e03dab552d66450d43ab82bda0a5a1)