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.
gl_common: factor context creation

Always create the context in mpgl_init(), instead of doing it when
mpgl_config_window() is called the first time. This is a small step
towards cleaning up the GL backend interface, and adding other things
like perhaps GLES support, or a callback-driven backend for libmpv.
Do not call strerror()

...because everything is terrible.

strerror() is not documented as having to be thread-safe by POSIX and
C11. (Which is pretty much bullshit, because both mandate threads and
some form of thread-local storage - so there's no excuse why
implementation couldn't implement this in a thread-safe way. Especially
with C11 this is ridiculous, because there is no way to use threads and
convert error numbers to strings at the same time!)

Since we heavily use threads now, we should avoid unsafe functions like
strerror().

strerror_r() is in POSIX, but GNU/glibc deliberately fucks it up and
gives the function different semantics than the POSIX one. It's a bit of
work to convince this piece of shit to expose the POSIX standard
function, and not the messed up GNU one.

strerror_l() is also in POSIX, but only since the 2008 standard, and
thus is not widespread.

The solution is using avlibc (libavutil, by its official name), which
handles the unportable details for us, mostly. We avoid some pain.
vo_opengl: Linearize non-RGB sRGB files correctly (eg. JPEG)

Signed-off-by: wm4 <wm4@nowhere>
mixer: don't show softvol neutral marker on OSD if not using softvol

Also fix the comment on the softvol field.
audio: fix busy loop when seeking while paused

When playing paused, the amount of decoded audio is limited to a small
amount (1 sample), because we don't write any audio to the AO when
paused. The small amount could trigger the case of the wanted audio
being too far in the future in the PTS sync code, which set the audio
status to STATUS_DRAINING, which in turn triggered the EOF code in the
next iteration. This was ok, but unfortunately, this triggered another
retry in order to check resuming from EOF by setting the status to
STATUS_SYNCING, which in turn lead to the busy loop by alternating
between the 2 states. So don't try resyncing while paused.

Since the PTS syncing code also calls ao_reset(), this could cause the
pulseaudio daemon to consume some CPU time as well.

This was caused by commit 33b57f55. Before that, the playloop was merely
run more often, but didn't cause any problems.

Fixes #1288.
audio: alternative fix for previous commit

This is a somewhat obscure situation, and happens only if audio starts
again after it has ended (in particular can happens with files where
audio starts later). It doesn't matter much whether audio starts
immediately or some milliseconds later, so simplify it.
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.
gl_video: minor simplification

Not needed anymore.
vo_direct3d: check whether D3DFMT_A8 is available

I suspect this is what is happening in github issue #1265 (at least
partially).

If D3DFMT_A8 is not available, fall back to RGBA. This is less efficient
in general, so we normally want to avoid it.
ao_wasapi: don't treat SetDisplayName() failure as fatal

Same for SetIconPath().
demux_mkv: fix a possible out of bounds access

The if branch has a weak check to test whether the codec_id is the short
ID, and handles the long IDs in the else branch. The long IDs are all
longer than 12 bytes long, so hardcoding the string offset to get the
trailing part of the name makes sense. But the if condition checks for
another thing, which could get the else branch run even if the codec_id
is short.

Fix the bogus control flow and check if the codec_id is long enough. One
of these checks could be considered redundant, but include them both for
defensive coding.
demux_mkv: cosmetics
demux_mkv: simplify extradata handling

It was more complicated than necessary.

The behavior changes slightly. Now it might pass through extradata when
it didn't before (hopefully harmless), and doesn't fail with an error if
extradata is not available, even though it's needed (harmless, will fail
either way).
subprocess-win: remove a Vista-only flag

PIPE_REJECT_REMOTE_CLIENTS isn't supported on XP. It's not really
needed, so remove it. Also fix error checking for CreateNamedPipe.
build: fix typos

thanks to @Nikoli
build: move --dvbin to TV features,  remove --dvb
build: move --cplayer to build options

This way it’s near to it’s libmpv counterparts
ao/wasapi: make get_device_delay return an error code
ao/wasapi: simplify the init retry