* ./include/vlc_threads_funcs.h, ./src/misc/threads.c: eradicated

    vlc_mutex_need() and vlc_mutex_unneed().
  * ./src/misc/variables.c: implemented VLC_VAR_MUTEX variables.
  * ./modules/misc/gtk_main.c, ./src/libvlc.c: replaced named mutexes with
    named mutex variables.