version.sh: fix git rev. generation (.git is not always a directory)

It appears git submodule handling recently changed, changing the .git
directory to a regular file containing submodule specific information.
This means that version.sh would generate "#define VERSION "git-UNKNOWN""
if the checkout is a submodule, because it explicitly checks for a .git
directory using test -d. Change it to -e so that this case is handled
correctly.
command: add command to show playlist on OSD
core: remove --edlout functionality

This could write .edl files in MPlayer's format. Support for playing
these files has been removed from mplayer2 quite a while ago. (mplayer2
can play its own, "new" .edl format, but does not support writing it.)

Since this is a rather obscure functionality, and it's not really clear
how it should behave (e.g. what should it do if a new file is played),
and wasn't all that great to begin with (what if you made a mistake?
the "edl_mark" command sucks for editing), get rid of it.

Suggestions how to reimplement this in a nicer way are welcome. If it's
just about retrieving timecodes, this in input.conf will do:

    KEY print_text "position: ${=time-pos}"
Remove BSD legacy TV/radio support (BT848 stuff)

FreeBSD actually supports V4L2, and V4L2 supports this chip. Also,
this chip is from 1997. Farewell.
ao_dsound: support 6.1 and 7.1 channel configurations

Instead of doing the channel reordering manually, use the existing
support in reorder_ch.c.

Untested.
mixer: prefer AO softvol control over volume filter

This partially reverts earlier decisions, when I thought it would
always be better to prefer the audio volume filter over the AO's,
because the AO's relies on the underlying audio-API, which could
be broken or exhibit unusual behavior (like it happened with ao_dsound).

However, since the audio buffer can be quite large (500 ms), and we
don't attempt to flush & refilter the audio on volume changes, always
prefer AO volume control (as long as the AO mixer doesn't control the
system mixer).

Also document what the mixer.c related AO fields mean (hopefully not
too brief).
audio/out: prefer ao_dsound over ao_portaudio

On Linux, ao_portaudio has weird freezing issues (possibly specific to
the ALSA backend, though). Also ao_dsound is more likely to get multi-
channel audio output right, and ao_portaudio probably mangles these.
video/out: change autoprobe order

Basically, move vo_opengl above the other VOs (except vo_vdpau). This
changes preferences on Windows and Linux.

Move vo_opengl_old further down and make it the last fallback (before
vo_x11).

vo_caca is crap (no pun intended), and should never be autoprobed.
audio/out, video/out: hide encoding VO/AO

mpv -ao help and mpv -vo help shouldn't show the encoding outputs (named
"lavc" on both cases). Also make it impossible to select these manually
when not encoding.