Apparently this is still problematic leading to errors like
`Qualifying with unknown namespace/class`. It seems that moving the enum to
a different header file works. The trick to use a macro to define
`enum class` ceased to work on the other hand.
Specifying a function with the namespace like
`void QtGui::FinalWizardPage::showResults()` leads to the same problem and
also needs to be avoided.
* Check directly whether changed properties contain a property
instead of checking indirectly whether the returned QVariant
is invalid.
* Avoid copying the QVariant.
* Effectively this should not change anything; the code is just
more readable and possibly more efficient.
Martchus