Fix ocl::filter2D.
In current implementation, this function only works when anchor point is
in the kernel center and kernel size supported is either 3x3 or 5x5.
Fix a bug of gfft.
When user provided corners buffer is big enough to be copied to from
tmpCorners_, we allow the buffer to be reused other than allocate a new
cl_mem object.
Merge pull request #935 from pengx17:2.4_filter2d_fix