Qnx: More descriptive error message for debug token check

Change-Id: I68a77ad494d50a169ee757485d4c31cbdfeea9b1
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
QmlDesigner: Don't drop anymore in a layoutable

The behavior to drop something in a layoutable is quite strange because
we don't support visual layouting at all.

Task-number: QTCREATORBUG-11543
Change-Id: I4d455d3a6f099edfeacbdb0def2e9e9c4489768c
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>