Fix bug with QMessageFolderId not being hashable.
Fix bug with QMessageFolderId not being hashable.

By adding _valid member variable, and using it instead of lazily
 instantiating d_ptr object.

kaltsi/qt-mobility,KDE/android-qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility,qtproject/qt-mobility,qtproject/qt-mobility,KDE/android-qt-mobility,enthought/qt-mobility,tmcguire/qt-mobility,kaltsi/qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility,KDE/android-qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,enthought/qt-mobility,enthought/qt-mobility,KDE/android-qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility,enthought/qt-mobility