use the new-style headers in the samples to improve OpenCV build time.

samples/c/contours.c

@@ -1,14 +1,5 @@
-#ifdef _CH_
-#pragma package <opencv>
-#endif
-
-#define CV_NO_BACKWARD_COMPATIBILITY
-
-#ifndef _EiC
-#include "cv.h"
-#include "highgui.h"
-#include <math.h>
-#endif
+#include <opencv2/imgproc/imgproc.hpp>
+#include <opencv2/highgui/highgui.hpp>
 
 #define w 500
 int levels = 3;