This patch enables usage of QAbstractItemModelTester on
QFileSystemModel. QAbstractItemModelTester called fetchMore()
on all items. QFileSystemModel represents the whole file system.
This led to very long test runs. To avoid this, this patch
introduces a new feature in QAbstractItemModelTester, namely
to disable calling of fetchMore().
Change-Id: Ie5d2e22fa4c143be7c080d9f79632cd2cbe07aac
Reviewed-by: David Faure <david.faure@kdab.com>