Parameter scans only supported with old diagnostics

[David Dickinson]

The target arrays etc. are only setup when old diagnostics is active (not the default).

[David Dickinson]

Note we do not check this when setting up the parameter scan module.

[David Dickinson]

Similarly ensemble_average only seems to support the old diagnostics (unless new diagnostics somehow updates the old diagnostics local data) so calculate_outputs in gs2_main might not be doing the same thing in all cases depending on the diagnostic route selected.