Fixed OpenCL DiffusionSolver. Lots of changes were required  - it was pretty much major code rewrite. Improved error detection/ error messages for solvers. Added option <DoNotScaleSecretion> to DiffusionSolverFE which makes it behave like flexible diffusion solver. Flexible Diffusion Solver is deprecated, but maintained. Added option to specify DiffusionField Name in the DiffusionField element e.g. <DiffusionField "Name"=FGF>  - this is the correct way of ensuring logical consistency of our XML . Old style XML with <FieldName> still works to ensure backwards compatibility