When scanning multiple lua scripts, create a new lua_State for each script. This will prevent data corruption from a previous script affecting subsequent scripts.

This patch
  - ensure that current playing item is properly detected
  - deactivate item changes since it is wrongly implemented
    (i_id from input_item_t and playlist_item_t are compared,
     which is wrong)

I didn't find any reason to do it, and it slows closing quite a lot,
if you know why we should do that, please speak up etc.

It closes #2349.

It simplify the flac decoder code.
It fixes the build of the packetizer when flac is disabled.
It makes the flac packetizer behaviour independant of the flac decoder presence.

Signed-off-by: Pierre d'Herbemont <pdherbemont@free.fr>

- keep root index of views when searching
- clear search when browsing or changing view
- layout and geometry fine tuning

Performs much better.
URL is sanitized by filename_sanitize() just as title before.

We may be joining the input_thread inside the vlm lock, and try to vlm lock inside the stop event handler.