Fix a debug message

This will help reduce useless process wakeups

* Don't find playlist
* Fix a few bugs in notification plugins

Todo: find a way to get rid of this mostly redundant code and rewrite the XOSD plugin

Don't remove AC_PROG_CPP our headerfile and library checking macros depend on it. Unbreak configure.ac

* various improvements to our Apple Remote bindings by the original author of the inofficial API, Martin Kahr (martin at his surname.com)

I'm far from being sure this is the right thing to do, but it allows MMSH to work correctly (it requests some data while the server is closing connection)

Do not search for playlist

Convert the new libvlc API (so, the one that is in src/control) not to use the old libVLC API (the one that is in libvlc.c, er, no, was... ah... maybe it's the internal one... err .... well, it's about vlc for sure...)

* instances creation/deletion stuff to libvlc-common.c
* implementation of the old libvlc API to libvlc.c

vlc_t => libvlc_int_t

Also, make it clearer what is shared and instance-specific

So,
libvlc_t ==> libvlc_global_t
vlc_t ==> libvlc_int_t (internal instance)

p_object->p_libvlc ==> p_object->p_libvlc_globale
p_object->p_vlc ==> p_object->p_libvlc

VLC_OBJECT_VLC ==> VLC_OBJECT_LIBVLC

And by the way, there is some cleanup required :) (ie, some things are created in the global object instead of the instance-specific one)