StencilI/StencilJ/StencilK should be handled as integers

[babrodtk]

The following

$ u@i,j@ = ( u_0@i,j+1@ ) $

should generate something like

grid.cellAt( i, j, u ) = (grid.cellAt( i, j+1, u_0 ))

NOTE: we do not want to generate j+ double(1).