Added 1 missing file to the kernel toolbox and minor changes to 2 files in the multigp toolbox.
Added 1 missing file to the kernel toolbox and minor changes to 2 files in the multigp toolbox.

SheffieldML/forkedGPmat,SheffieldML/forkedGPmat,SheffieldML/forkedGPmat,SheffieldML/forkedGPmat,SheffieldML/forkedGPmat,SheffieldML/forkedGPmat