* ./include/modules_inner.h, ./src/misc/configuration.c: support for config

  * ./include/modules_inner.h, ./src/misc/configuration.c: support for config
    options callbacks.

    They don't take any argument for the moment, but this will change when
    I'm finished with my other vlc changes. There is a little problem: the
    Gtk+ interface keeps calling Put***Variable each time we click on "Apply"
    or "Save". I think it should only call it once. Is there a way to fix
    this? Gildas? lool? :-)