Update the OpenCL documents.
fix three warning about mog, mog2 and KNearestNeighbour.
fix warning about addWeighted and remove magnitudeSqr().
fix for bug #3291:

add INSTALL command for TBB target
fixed ocl::minMax
fixed ocl::countNonZero
Missing closedir with opendir
Make libv4l support optional for testing purposes.
fixed ocl::sum, ocl::sqrSum, ocl::absSum
fixed ocl::phase
Merge pull request #1522 from nghiaho12:latentsvm
Merge pull request #1518 from jet47:bug-3291-tbb-install
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