When accessing global memory by DWORD4, memory bandwidth
can be fully utilized on Intel platform. This patch will
make more image format(e.g. 8UC4) be processed in DWORD4
by work-item. After applying this patch, 3 subcase of
./opencv_perf_core --gtest_filter=OCL_RepeatFixture_Repeat.Repeat/*
can be speedup on HD4000 graphics card with Beignet:
OCL_RepeatFixture_Repeat.Repeat/2, 64% improvement.
OCL_RepeatFixture_Repeat.Repeat/6, 50% improvement.
OCL_RepeatFixture_Repeat.Repeat/8, 56% improvement.
Signed-off-by: Chuanbo Weng <chuanbo.weng@intel.com>

There is necessary to account also x-coordinate of the end of the edge when determining bounding box of the edge collection.

- Use cv::AutoBuffer rather than new allocation
- Fix "assignment operator could not be generated" warning

mask = cv2.inRange(hsv, lower_green, upper_green)
to
mask = cv2.inRange(hsv, lower_blue, upper_blue)

Rewrite the note on HoughCircles documentation to make it more clear

Add note to clarify that the output vector of found circles is sorted by
descending order of centres accumulator values.

Also delete reductant lines on the HoughCircles documentation.

Added comments to hough circles function.

Added comments to icvhoughgradient

Misalignment in line 1183 corrected

It could improve performance when image size is large.
E.g. OCL_PyrUpFixture_PyrUp.PyrUp/18