* FIX INF_ENGINE RELU ERROR

* set slope to variable

* tab in indentwq

modules\dnn\src\layers\prior_box_layer.cpp(208): warning C4834: discarding return value of function with 'nodiscard' attribute

* Resolves 6125

* Fix test code

* Delete unnecessary code

to avoid accessing of 'p[-1]' (static code analysers dislike this)

Arm: fix the test failure of OCL_Imgproc/CLAHETest.Accuracy on ODROID-XU4 (#11409)

* fix the test failure of OCL_Imgproc/CLAHETest.Accuracy on ODROID-XU4
  * avoid the race condition in the reduce

* imgproc(ocl): simplify CLAHE code

* remove unused class

OpenCV 3.4.1 for Intel Computer Vision SDK

for cv::Mat with type=16UC3 and width < 16

std::exception_ptr requires enabled C++11 mode

- remove duplicates
- restore "always on" missing entries
- fix FP16 detection on MSVC

for cv::Mat with width < 16