Change ocl::Canny test case category
Test code clean up.
Format ocl::Canny header
Fix a bug of ocl::Canny when src/dst using the same buffer.
Remove unused kernels.
Fix a potential bug of ocl::CannyBuf.

The program would crash if release is called twice.
Remove my test codes.
Merge pull request #805 from pengx17:master_canny_fix