Feature13Installer.cls

public class Feature13Installer extends InstallHandlerBase {
    public override Version GetLastPackageVersionWithoutFeature () {
        return new Version (1,2);
    }

    public override void OnFreshInstall (InstallContext context) {
        InitializeFeature13();
    }
    public override void OnUpgradeFromOldPackage (InstallContext context) {
        UpgradeForFeature13();
    }
}