known issues:

  - gst-launch-0.10 videotestsrc ! "video/x-raw-yuv, format=(fourcc)YV12" ! glimagesink
    -> wrong color on linux
    ok it comes from hardware, it seems that on ati+win32 it works, 
    but on nvidia+linux we do not need to make a disctinction between I420 and YV12
    (see comments in gst/gl/gstgldisplay.c line 256 and line 2426)