Up until now, 'GD.Print' would convert parameters first to
Variant and only then to String. This meant parameters that cannot be
converted to Variant would be printed as "Null".
This commit makes 'GD.Print' fallback to 'System.Object.ToString()'
if the parameter could not be converted to Variant.
The same applies to all 'GD.Print' variants:
'GD.PrintS', 'GD.PrintT', 'GD.PrintErr' and 'GD.PrintRaw'.