y4mhist.c:481:14: warning: variable pheight set but not used
y4mhist.c:481:6: warning: variable pwidth set but not used
y4mhist.c:480: warning: variable do_vectorscope set but not used
y4mhist.c:479:21: variable ss_h set but not used
y4mhist.c:479:15: warning: ss_v set but not used
need to have SDLgfx which apparently few systems have anymore - so those
variables aren't needed most of the time
