Use the QStandardItemModel workaround until 5.1.0.

If there is a Qt 5.0.3 release, it may or may not contain the patch
that fixes this issue.

 http://thread.gmane.org/gmane.comp.lib.qt.releasing/882

Just use the workaround until 5.1.0 which certainly will contain the
fix. Don't use the workaround before Qt 5.0.0.
Merge topic 'expand-version-of-Qt5-gui-fix' into next

7a24f12 Use the QStandardItemModel workaround until 5.1.0.