ffplay: simplify and fix flushing out old subtitles on seeking

Fixes the additional issue reported in ticket #2666.

Signed-off-by: Marton Balint <cus@passwd.hu>
examples/muxing: remove useless instruction

Simpler and less confusing.
examples/Makefile: disable -O2 optimizations

There is no much point in optimizing example code, and the -O2 flag is
annoying when debugging.
lavc/utils: improve feedback in case of invalid packet size
lavf/mux: rename variable cortag -> tagbuf2 in init_muxer()

Possibly enhance readibility.
lavf/movenc: improve error feedback in case malformed AAC bitstream is detected

Consistent with the FLV muxer.
doc/bitstream-filters.texi: add documentation for the aac_adtstoasc filter

Based on the notes in libavcodec/aac_adtstoasc_bsf.c.
doc/bitstream_filters: document the chomp filter

TODO: add some meaningful examples.
examples/muxing: rename audio/video_pts to audio/video_time

The new name is less confusing, since the variables represent times
rather than timestamps.
ffprobe: simplify branching logic in probe_file()
ffprobe: fix exit code with stream specifiers

Without this fix, ffprobe would exit with a failure exit code if a stream
specifier is given that selects the last stream.

Signed-off-by: Nicolas George <nicolas.george@normalesup.org>
ffprobe: reindent after previous commit
ffprobe: always exit 1 in case of errors

This is consistent with the other ff* tools, and also avoids spurious
success reports when ret%256 = 0.
Merge remote-tracking branch 'cus/stable'

* cus/stable:
  ffplay: simplify and fix flushing out old subtitles on seeking

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