Add OpenCV include to pch file

Author: BloodAxe

Chapter2_iPhoneAR/Example_MarkerBasedAR/Example_MarkerBasedAR/Example_MarkerBasedAR-Prefix.pch

@@ -8,6 +8,10 @@
 #warning "This project uses features only available in iOS SDK 5.0 and later."
 #endif
 
+#ifdef __cplusplus
+    #include <opencv2/opencv.hpp>
+#endif
+
 #ifdef __OBJC__
   #import <UIKit/UIKit.h>
   #import <Foundation/Foundation.h>