ShowSourcePackages
if (!specification->ShowSourcePackages())
fShowSourcePackages = value->ShowSourcePackages();
if (!fSource.IsSet() || fSource->ShowSourcePackages() != value) {
&& fShowSourcePackages == other.ShowSourcePackages()
bool ShowSourcePackages() const;
fShowSourcePackagesItem->SetMarked(packageFilterSpecification->ShowSourcePackages());
fModel.FilterSpecification()->ShowSourcePackages());