ShowInstalledPackages
if (!specification->ShowInstalledPackages())
fShowInstalledPackages = value->ShowInstalledPackages();
if (!fSource.IsSet() || fSource->ShowInstalledPackages() != value) {
&& fShowInstalledPackages == other.ShowInstalledPackages()
bool ShowInstalledPackages() const;
fShowInstalledPackagesItem->SetMarked(packageFilterSpecification->ShowInstalledPackages());
fModel.FilterSpecification()->ShowInstalledPackages());