cpp verison of StereoRectify is wrong (Bug #1338)

Here is some code where if you run stereoRectify on same intrinsics/extrinsics from stereoCalibrate(), when get weird P1 and P2, but if you calcualte them using stereoRectifyUncalibrated they work (but the fx/fy in the two projection matricies are no longer equal, which isn't the best -- I know some code just looks at fx/fy in one of the two matrices and assumes they are equal).

 1Mat R1, R2, P1, P2, Q;
 2Rect validRoir2;
 3
 4stereoRectify(cameraMatrixr0, distCoeffsr0,
 5          cameraMatrixr1, distCoeffsr1,
 6          imageSize, R, T, R1, R2, P1, P2, Q,
 7          0, imageSize, &validRoir0, &validRoir1, CV_CALIB_ZERO_DISPARITY);
 8
 9    Mat rmapr2r2;
10// IF BY CALIBRATED (BOUGUET'S METHOD)
11    if( useCalibrated )
12    {
13        // we already computed everything
14
15      //BUT P1 and P2 have REALLY large numbers and are correct.
16
17    }
18// OR ELSE HARTLEY'S METHOD
19    else
20 // use intrinsic parameters of each camera, but
21 // compute the rectification transformation directly
22 // from the fundamental matrix
23    {
24        vector<Point2f> allimgptr2;
25        for( k = 0; k < 2; k++ )
26        {
27            for( i = 0; i < nimages; i++ )
28                std::copy(imagePoints[k][i].begin(), imagePoints[k][i].end(), back_inserter(allimgpt[k]));
29        }
30        F = findFundamentalMat(Mat(allimgptr0), Mat(allimgptr1), FM_8POINT, 0, 0);
31        Mat H1, H2;
32        stereoRectifyUncalibrated(Mat(allimgptr0), Mat(allimgptr1), F, imageSize, H1, H2, 3);
33
34        R1 = cameraMatrixr0.inv()*H1*cameraMatrixr0;
35        R2 = cameraMatrixr1.inv()*H2*cameraMatrixr1;
36    P1 = Mat::zeros(3, 4, CV_64F);
37    P2 = Mat::zeros(3, 4, CV_64F);
38
39    for (uint i=0;i<3;i++)
40      for (uint j=0;j<3;j++) {
41        P1.at<double>(i,j) = cameraMatrixr0.at<double>(i,j);
42        P2.at<double>(i,j) = cameraMatrixr1.at<double>(i,j);
43      }
44    P2.at<double>(0,3) = P2.at<double>(0,0)*T.at<double>(0,0);
45
46    // P1 and P2 are now good but P1(0,0) != P2(0,0) (same for
47    // (1,1)) would like them to be the same.
48
49    }