Add a runtime check and configure warning to disable KDE4 native
file pickers, if the Qt4 glib dispatcher doesn't honor the
QEventLoop::ExcludeSocketNotifiers flag.

This way polling the QClipboard using the event loop won't
crash LibreOffice with recursive paint events,

See https://bugreports.qt-project.org/browse/QTBUG-37380

Change-Id: I5cad30ead74571e49a075c084cca7a19acff7523