x11: rely on the Atom cache

XInternAtom() has a 64 entry hash table to avoid network accesses. Rely
on this cache, instead of caching these manually.
vo_opengl: minimal EGL on X11 support

Pretty useless and only good for testing.

Does not include any form of GLES support.
player: fix --secondary-sid

Use the "default" selection for the ff-index, not the "no" selection.

Broken by commit f0f83ff.
Fixes #1243.
video: get hwaccel flag from pixdesc
video: refuse to allocate image data for hwaccel formats

Makes no sense.
video: handle endian detection in a more generic way

FFmpeg has only a AV_PIX_FMT_FLAG_BE flag, not a LE one, which causes
problems for us: we want to have the LE flag too, so code can actually
detect whether a format is non-native endian. Basically, we want to
reconstruct the LE/BE suffix all AV_PIX_FMT_*s have.

Doing this is hard due to the (messed up) way AVPixFmtDescriptor works.
The worst is AV_PIX_FMT_RGB444: this group of formats describe an
endian-independent access (since no component actually spans 2 bytes,
you only need byte accesses with a fixed offset), so we have to go
through some pain.
video: passthrough unknown AVPixelFormats

This is a rather radical change: instead of maintaining a whitelist of
FFmpeg formats we support, we automatically support all formats.

In general, a format which doesn't have an explicit IMGFMT_* name will
be converted to a known format through libswscale, or will be handled
by code which can treat pixel formats in a generic way using the pixel
format description, like vo_opengl.

AV_PIX_FMT_UYYVYY411 is a special-case. It's packed YUV with chroma
subsampling by 4 in both directions. Its component order is documented
as "Cb Y0 Y1 Cr Y2 Y3", meaning there's one UV sample for 4 Y samples.
This means each pixel uses 1.5 bytes (4 pixels have 1 UV sample, so
4 bytes + 2 bytes). FFmpeg can actually handle this format with its
generic mechanism in an extremely awkward way, but it doesn't work for
us. Blacklist it, and hope no similar formats will be added in the
future.

Currently, the AV_PIX_FMT_*s allowed are limited to a numeric value of
500. More is not allowed, and there are some fixed size arrays that need
to contain any possible format (look for IMGFMT_END dependencies).

We could have this simpler by replacing IMGFMT_* with AV_PIX_FMT_*
through the whole codebase. But for now, this is better, because we
can compensate for formats missing in Libav or older FFmpeg versions,
like AV_PIX_FMT_RGB0 and others.
video: add image format test program
video: remove aliases for some rarely referenced image formats

These formats are still supported; you just can't reference them via a
defined constants directly. They are now handled via the generic
passthrough.

(If you want to use such a format, you either have to add the entry
back, or use AV_PIX_FMT_* directly.)
vo_wayland: don't use endian-specific defines

Instead, use the native-endian alias, and switch the wayland format
depending on the target platform's endian.

This drops support for swapped-endian formats, but I think that is ok.
Not only are the affected formats rather ancient and backwards, but
using swapped formats probably does not make any sense for performance
either.

Untested.
video: remove swapped-endian image format aliases

Like the previous commit, this removes names only, not actual support
for these formats.
demux: report 0s readahead time as fallback in some situations

If no packets are queued, the readahead time is obviously 0.

If the end time is smaller than the start time, the problem is probably
that audio and video start at slightly different times - report 0 in
this case too.

Do this because seeing "???" as readahead time is a bit annoying.
command: use playback time as reference for sub_seek

update_subtitle() already uees playback_pts to make subtitles work
better in no-audio mode. Using get_current_time() usually gets
playback_pts, but also has the advantage that it will use the seek
target time during seeks. This will result in multiple sub_seek commands
doing the right thing (at least as long as they're far enough apart so
that seeking is actually initiated when the second command is run).
demux_mkv: index all packets

Instead of indexing only 1 packet per cluster (which is enough for
working seeking), add every packet to the index.

Since on seek, we go through every single index entry, this probably
makes seeking slower. On the other hand, this code is used for files
without index only (e.g. incomplete files), so it probably doesn't
matter much.

Preparation for the following commits.
demux_mkv: read CueRelativePosition/CueDuration elements

Nothing is done with them yet. This is preparation for the following
commit.

CueRelativePosition isn't even saved anywhere, because I don't intend to
use it. (Too messy for no gain.)
demux_mkv: apply subtitle preroll only if needed, based on cue index

The demuxer has a hack to seek to the cluster before the target cluster
in order to "catch" subtitle lines that start before the seek target,
but overlap with the video after the seek target.

Avoid this hack if the cue index indicates that there are no overlapping
subtitle packets that can be caught by seeking to the previous cluster.
demux_mkv: for subtitle preroll, consider all clusters

This considered only index entries that were for the same track ID as
the track used for seeking. This doesn't make much sense for preroll;
it'll just possibly skip clusters, and select an earlier cluster.

One possible negative side-effect is that the preroll might be too tight
now, and miss subtitle packets more often.
demux_mkv: fix indentation

Meh.
sub: load .mks files as external subtitles
audio/out/push: when using audio wait fallback, recheck condition

If calling ao->driver->wait() fails, we need to fallback to timeout-
based waiting. But it could be that at this point, the mutex was already
released (and then re-acquired). So we need to recheck the condition in
order to avoid missed wakeups.

This probably wasn't an actually occurring problem, but still could
cause a small race-condition window if the dynamic fallback is actually
used.