* ./src/libvlc.c, ./include/main.h: the root of all objects is now

  * ./src/libvlc.c, ./include/main.h: the root of all objects is now
    p_libvlc, and each p_vlc is a child of p_libvlc. Reasons for this are:

     o the module bank and the message bank only need to be initialized once,
       which gives faster loads when multiple instances of libvlc are used,
     o we allow the possibility of different p_vlc sharing objects, for
       instance the audio output,
     o the CPU detection is only done once.

    This patch is not polished yet, but I cannot do any intensive tests for
    the moment because of a bug somewhere that leaves audio output objects
    lying here and there which needs to be investigated first. The current
    major issue is that the module bank is no longer freed.