CDB: Fix assigning a Qt5 QString.

Task-number: QTCREATORBUG-13173
Change-Id: I8d60a3e2bcc6e6b67cde7238cad356a43bd8aa92
Reviewed-by: Christian Stenger <christian.stenger@digia.com>
Squish: Fix tst_rename_file

Change-Id: Ic5aab61b2bc73f4de737b81d59fea0189893adfd
Reviewed-by: Robert Loehning <robert.loehning@digia.com>