ItemIsTristate means QTreeWidget determines the check state of parent
items based on the check state of child items.
Checking/unchecking the parent propagates to children; but setting
the parent to PartiallyChecked shouldn't do that, especially since it can
lead to children without ItemIsTristate having PartiallyChecked check state.
Change-Id: Ibc8b7c77d9ec4c1578c07f3c62581edb770f8439
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@theqtcompany.com>
dd23d9f161