vo_opengl: something

Insert explanation here.

Fixes #1023.
vo_opengl: fix srgb with certain inputs

Sampling from the source texture and scaling must always be done
separately in this mode.

Fix suggested by haasn.

Still looks a bit wrong, though.
mixer: don't show softvol neutral marker on OSD if not using softvol

Also fix the comment on the softvol field.
command: sub_add with "auto" should not always select a subtitle track

Running "sub_add file.srt auto" during hook execution automatically
selected the first added track. This happened because all tracks added
with sub_add are marked as "external", and external subtitles are always
selected by default.

Fix this by negating the "external" flag when autoselecting subtitles
during loading. The no_default flag exists for this purpose; it was
probably added for libquvi originally, where we had the same issue.
player: simplify and fix ordered chapter EOF handling

Ordered chapter EOF was handled as special-case of ending the last
segment. This broke --kee-open, because it set AT_END_OF_FILE in an
"inconvenient" place (after checking for --keep-open, and before the
code that exits playback if EOF is reached).

We don't actually need to handle the last segment specially. Instead, we
remain in the same segment if it ends. The normal playback logic will
recognize EOF, because the end of the segment "cuts off" the file.

Now timeline_set_from_time() never "fails", and we can remove the old
segment EOF handling code in mp_seek().
options: fix swapped deprecated/replacement in warning

This was relevant for --af and --vo (both use this option type, and have
deprecated aliases).
options: fix channel map options sometimes failing

Channel amp otpions were not copied correctly: it copied the size of a
pointer to struct chmap, not the struct itself. Since mp_chmap is
currently 9 bytes, this meant the last channel entry was not copied
correctly on 64 bit systems, leading to very strange failures. It could
be triggered especially when using the client API, because the client
API always copies options on access (mpv command line options tend to
work directly on options).
ao_coreaudio: initialize fetched properties to zeros

Should hopefully fix #1249 and #1279
vo_opengl: make operator precedence explicit

More readable.
vo_opengl: Reword comment in shader

I didn't quite understand this comment after looking at the code again
months later, so I reworded it for better clarity.
vo_opengl: Linearize non-RGB sRGB files correctly (eg. JPEG)

Signed-off-by: wm4 <wm4@nowhere>