fixed many warnings from GCC 4.6.1

samples/c/mser_sample.cpp

@@ -68,7 +68,7 @@ int main( int argc, char** argv )
 		for ( int j = 0; j < (int)r.size(); j++ )
 		{
 			Point pt = r[j];
-			img.at<Vec3b>(r[j]) = bcolors[i%9];
+            img.at<Vec3b>(pt) = bcolors[i%9];
 		}
         
         // find ellipse (it seems cvfitellipse2 have error or sth?)

samples/cpp/video_homography.cpp

@@ -39,7 +39,6 @@ namespace
             {
                 Point2f pt_new = query[matches[i].queryIdx].pt;
                 Point2f pt_old = train[matches[i].trainIdx].pt;
-                Point2f dist = pt_new - pt_old;
 
                 cv::line(img, pt_new, pt_old, Scalar(125, 255, 125), 1);
                 cv::circle(img, pt_new, 2, Scalar(255, 0, 125), 1);