fixed bug with simplex initialization in Downhill solver (thanks to Toby Rule for the patch): http://code.opencv.org/issues/3990.
re-enabled Downhill solver test, let's see how it goes

fixed http://code.opencv.org/issues/3935
possibly fixed http://code.opencv.org/issues/3594

fixed invalid output of cv::dft when using DFT_ROWS + DFT_COMPLEX_OUTPUT (http://code.opencv.org/issues/3428)

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

Conflicts:
	modules/contrib/include/opencv2/contrib/retina.hpp

Conflicts:
	cmake/OpenCVFindLibsVideo.cmake

The two functions featuring nNull are not particularly needed, so
I simply removed them.

Conflicts:
	modules/highgui/src/cap_msmf.hpp

Conflicts:
	modules/gpu/perf/perf_imgproc.cpp

Cast a long integer to double explicitly.

Conflicts:
	modules/python/src2/cv2.cpp

Cast some matrix sizes to type int.

Change some vector mask types to unsigned.

Conflicts:
	modules/core/src/arithm.cpp

Conflicts:
	modules/highgui/src/window_QT.cpp

A difference of two pointers was casted to unsigned which can lead to
overflow on 64-bit systems.

If used cl compiler, but generator is not Visual Studio e.g. Ninja,
enable FS option to prevent blocking PDB file in multithreaded build.

The use of built-in CMAKE_CURRENT_LIST_DIR requires at least
CMake 2.8.3. This fix properly defines the variable to allow its
use in versions < 2.8.3 as well.

Fixes issue #4205.

Exclude >= 2.8.3 from reimplementation of CMAKE_CURRENT_LIST_DIR

This avoids violation of possible future CMake policy checks
regarding reserved/read-only variables.

Conflicts:
	doc/tutorials/imgproc/imgtrans/hough_lines/hough_lines.rst