Bug #2967, basic_structures.rst, fix 2 typos
Bug #2967, void DescriptorMatcher::radiusMatch() // description unclear,
only file:  common_interfaces_of_descriptor_matchers.rst
Bug #2966, insert CV_Assert(size.width>0 && size.height>0); in imshow()
(tab to space) 2x
(typo)
Include the OpenCV config headers into every module.

This has no bearing on compilation, but it makes them show up in IDEs.
added missing BackgroundSubtractorMOG2 parameters
Add ocl CLACH implementation.
Test cases (accuracy and performance) are provided.
Merge pull request #903 from aks2:2.4
Merge pull request #973 from pengx17:2.4_oclclahe
Merge pull request #980 from SpecLad:include-config
Merge pull request #972 from jet47:mog2-params-bug-2168