tests

- Beware that this only prints values on the printing processor in
parallel (rank 0 processor by now).

- Could also have added SubItem{Value,Array}PerItem outputs and
DiscreteFunctionP0, but it remains unclear to me if this development
is really relevant, due to the parallel defect of this
functionality. In the case of DiscreteFunctionP0, one can use the
DiscreteFunctionP0::cellValues() function to print values.