Qt: correctly split options and escape ':' so if your dshow devices or your subtitle contains a " :" in the name, it is correctly opened.

Thread initialization has changed in 2.7, such that VLC and Qt4 cannot
both use libxml2. While this maximum version requirement is bound to
frustrate Linux/BSD users, we cannot fix this within VLC. Falling back
to xtag is not quite as bad as crashing.

We need libxml version 2.5 for text reader.
pkg-config is present since version 2.3 at least (over 8 years ago).

Do not decode non reference pictures while prerolling.
It improves seek performance when decoding with ffmpeg.

It should fix/workaround https://bugs.launchpad.net/ubuntu/+source/vlc/+bug/324911
but I am not sure if it is the right way.

Qt: match the access changes for cdda-track specification (commit 55e3dca3 by fenrir )

- Trash Audio
- Keep original Audio

It is cleaner to not send event from caller threadand will fix a deadlock in the
playlist code.