If device does not support double, returns immediately.
Double floating points are not default supported by OpenCL.
Update the OpenCL documents.
fix three warning about mog, mog2 and KNearestNeighbour.
fix warning about addWeighted and remove magnitudeSqr().
fixed ocl::minMax
fixed ocl::countNonZero
Add opencl svm.
fix build error
Fix new blank line at EOF.
fixed ocl::sum, ocl::sqrSum, ocl::absSum
fixed ocl::phase
fixed ocl::setIdentity
Merge pull request #1509 from perping:2.4_docs
fixed ocl::meanStddev and created accuracy test for this function
Merge pull request #1457 from pengx17:2.4_oclsvm
perf test: update error message about relative error
fixed and extended ocl::norm
perf tests: added SANITY_CHECK_NOTHING()
ocl: perf test: disable MOG2 (random hungs), enable upload/download
Merge pull request #1530 from alalek:perf_tests_sanity_check_nothing