I thought this was a serious bug in the renderer, but it turned out to
be qmlscene just overriding the surface format without requesting the
needed depth and stencil buffers. An easy mistake to make, hence
introduce the warning.

Task-number: QTBUG-29037
Change-Id: I59d09d1b2a139e3add851777ff2eeb6c4efb47ec
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>