* don't try to stat() the dvd drive letter on win32
* disabled YUV overlay double buffering for now, as it seems to actually be
    slower.
* temporary fix in vlc_cond_signal() for win32 (I really should use
    SignalObjectAndWait() on WinNT so we can avoid race conditions in the
    pthread code). This fixes a problem noticed on WinXP where vlc would
    freeze regularly and eat-up all the CPU (fun no?)