Enable "useProvidedKeypoints" flag on cuda::ORB's detectAndCompute function in order to able to describe provided keypoints.

* additional author : Ender Tunç <endertunc@yahoo.com>

resolves #6473

 * Enable "useProvidedKeypoints" flag on cuda::ORB's detectAndCompute function in order to able to describe provided keypoints.

   Update for using 'const' reference to avoid array copy on each iteration.

resolves #6473

	Update for 'const' reference to avoid array copy on each iteration.

  * fix issue #6536
  * increase threshold in particular tests due to the difference of fmsub and fsub

  * modify test, too

Command line generation routine uses "-isystem" to include headers outside of "<opencv>/modules" folder, but GCC 6 does not work when passed "-isystem /usr/include" option.

  * fix issue 6521
  * use correct comparison

All of these: (performance) Prefer prefix ++/-- operators for non-primitive types.
[modules/calib3d/src/fundam.cpp:1049] -> [modules/calib3d/src/fundam.cpp:1049]: (style) Same expression on both sides of '&&'.

Add documentation for Kernel::run

Add OpenCL  support to linearPolar & logPolar.
The OpenCL code use float instead of double, so that it does not require
cl_khr_fp64 extension, with slight precision lost.

Add explicit conversion

Add explicit conversion from double to float to eliminate warning during
compilation.

Allow configuration of the square size in stereo_calib.

https://github.com/Itseez/opencv/issues/6456