stream: reconnecting doesn't make sense if stream is not seekable

This stops mpv from being stuck in reconnecting at the end of the file
with some unseekable streams.

Test URL: http://playerservices.streamtheworld.com/pls/CBC_R1_VCR_H.pls
player: fix quvi 0.9 playlist loading

The code made no sense at all.

Conflicts:
	mpvcore/player/loadfile.c
tools: add --no-cache --no-config to mpv_identify.sh
vo_opengl: reserve 4 texture units for video instead of 3

Video has up to 4 textures, if you include obscure formats with alpha.
This means alpha formats could always overwrite the first scaler
texture, leading to corrupted video display. This problem was recently
brought to light, when commit 571e697 started to explicitly unbind all 4
video textures, which broke rendering for non-alpha formats as well.

Fix this by reserving the correct number of texture units.
stream_lavf: support more libavformat protocols
manpage: fix incorrect default for --osc
input.conf: clarify the magic how default key bindings are added

This is a confusing mechanism, so the explanation should bit more clear.
osdep: handle SIGTERM

There's no reason why we should e.g. handle SIGQUIT, but not SIGTERM.

Note that sending SIGTERM twice still kills the player.
audio: fix bogus audio format comparison
Release 0.2.3