Also:
- Silence clang warnings about unsupported command line arguments
- Add diagnostic print to calib3d test
- Fixed perf test relative error check
- Fix iOS build problem

fixed mjpeg encoder so that libjpeg-based decoder does not complain on extra bytes in the end of stream

- fixes the Calib3d_StereoCalibrate_C testcase.
update comment regarding cv::SVD::MODIFY_A

Should fix #4191 (http://code.opencv.org/issues/4191)