Fixes bug for supposedly "self-containing" components.  Some components push
their context twice, once for a rerender but then again if that is implemented
as unrender/render.  In that case, we set the render container for the first
(rerender), but shouldn't set it again the second time (render), because it
would seem to be itself.

@bug W-2250051, W-2257715@
@rev goliver@
Merging origin/fabbott/master-pending/selfcontain into master