DOCS: mark the recent release in client-api-changes.rst

Also add instructions to release-policy.md, since this can be easily
forgotten.

CC: @mpv-player/stable
vo_vdpau: fix screenshots with anamorphic video

Fixes #1007.

CC: @mpv-player/stable
vdpau: correctly mark invalid mixer as such on vdp_video_mixer_create() failure

Otherwise vdp_video_mixer_destroy() would later fail when called on an invalid
video mixer handle. With mesa r600 vdpau driver, this would cause a segfault.
player: don't quit with --loop-file

Fixes #1009.

CC: @mpv-player/stable
wayland: pointer interface is created after theme

Just always load the theme. It gets freed properly and dosn't bother anyone.

Fixes #1012.

CC: @mpv-player/stable
TOOLS/zsh.pl: properly return non-zero when no matches are found

Returning a non-zero value signals to the zsh completion system that no matches
were added by the script so that it can try the user-defined matchers (e.g.
those defined with matcher-list).

Fixes #1008.
TOOLS/zsh.pl: properly set the return value

The previous commit made the completion script always return non-zero, even when
a match is found. This explicitly sets the return value to zero whenever a match
is found but defaults to non-zero in case nothing is matched.
TOOLS/zsh.pl: fix a ret that hadn't been changed to rc
TOOLS/zsh.pl: protect global environment
manpage: fix opengl-hq defaults

The FBO format was changed some time ago.

CC: @mpv-player/stable
etc/mpv.desktop: add audio/flac mimetype

Fixes #1025.

CC: @mpv-player/stable
manpage: remove duplicated content

Probably be accidentally added in b6b8bffd.

CC: @mpv-player/stable
Signed-off-by: wm4 <wm4@nowhere>
player: don't clobber playback position on video end

If video reaches EOF, and audio is also EOF (or is otherwise not
meaningful, like audio disabled), then the playback position was briefly
set to 0. Fix this by not trying to use a bogus audio PTS.

CC: @mpv-player/stable (maybe)
options: compatibility hack for --slave-broken

Seems some programs were still relying on it. Whatever, it's not hard to
support.

CC: @mpv-player/stable
coreaudio_device: fix overwriting of user input

Fixes #1030
Release 0.5.1