This fixes those annoying messages:
[00000307] main audio output debug: audio output is starving (38397), playing silence
[00000307] alsa audio output debug: recovered from buffer underrun
and sound becomes just fine.
Tested on 32bit and x86_64 systems.

* modules/audio_filter/channel_mixer/simple.c: revert mistaken commit of simple.c (aac channel order fix keeps haunting me)

* modules/demux/mkv.cpp: backport [19988] apply open probes when checking .mkv in same folder; fix memleak and fix crash when there are multiple .mkv and one of them is corrupt or incomplete

* modules/codec/faad.c: revert [25155] channel order fix since it needs more than also backporting [23226] simple.c so revert for now until we have something that applies to bugfix

* mozilla/control/npolibvlc.cpp: backport [25203] fixed name argument in add(url, name, options) for mozilla

* extras/contrib/src/Makefile: update x264 to latest revision (736) and backport darwin patch [24127] to match revision (trunk uses latest too); several memleaks fixed, minor bugfixes, few Altivec improvements, amd64 and FreeBSD support fixes

NEWS: remove FIXME on plugins, change SA number for MP4 issue; prepare for release based on what we have to keep things upto speed..

configure.ac: backport [24902] use build_os instead of SYS for detecting cygwin for hostname check because when we deal with mingw32 compiler (mno-cygwin mode) then SYS value isn't cygwin but (forced to) mingw32

Backport [23166] [23170] [23182] [23183] [23483] [23526] [23527] [23596]: Several live555 demuxer fixes.