added performance validation check
Added tests for Image2D
Optimize OpenCL version of StereoBM function
Fix problems on NVidia devices.
ocl: restore clFinish() in unmap() for AMD devices

This reverts commit 7d91b8efcd053304e5b0fb5afff06e151b2d4096.
Added extra checks to ocl::Image2D
Merge pull request #3368 from alalek:amd_clfinish
Merge pull request #3284 from vbystricky:oclopt_stereoBM
Merge pull request #3342 from alalek:perf_stability_check
Merge pull request #3367 from akarsakov:ocl_image2d