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

samples/cpp/starter_video.cpp

@@ -7,7 +7,8 @@
  * A starter sample for using opencv, get a video stream and display the images
  * easy as CV_PI right?
  */
-#include <opencv2/opencv.hpp>
+#include <opencv2/highgui/highgui.hpp>
+#include <iostream>
 #include <vector>
 
 using namespace cv;