avconv: drop additional strerror fallback

strerror_r is called by av_strerror already.
avconv: report the error for codec open failure

External codec may have corner case reason to fail at init, better
report them instead having the user wonder.
ogg: relax demuxer conformance checks

Some samples in the wild are missing headers that are expected by the
specification but in practice do not affect decoding.
configure: More msvc/icl combining

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Merge commit '1e340af8d6a97cc013a2ad8ba77c77129625a34f'

* commit '1e340af8d6a97cc013a2ad8ba77c77129625a34f':
  avconv: drop additional strerror fallback

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '42cc6cefd315c1556e2a52f7ebe2f766ec82b790'

* commit '42cc6cefd315c1556e2a52f7ebe2f766ec82b790':
  avconv: report the error for codec open failure

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'f963f701d90bd7bb03e39aab4e59bd137084e082'

* commit 'f963f701d90bd7bb03e39aab4e59bd137084e082':
  ogg: relax demuxer conformance checks

Conflicts:
	libavformat/oggdec.c

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

* qatar/master:
  configure: More msvc/icl combining

Merged-by: Michael Niedermayer <michaelni@gmx.at>
vp8: wait for prev_frame to parse segment_map before reading it.

This fixes occasional failures of vp8-test-vector-010 with frame-level
multithreading enabled.

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