problem with overlay views using multiple render graphs in the same window

[theodoregoetz]

In PR #309 I tried to split up the multiviews example into separate render graphs. The problem this example shows is that the secondary rendergraph clears the whole screen instead of it's designated smaller render area and I'm not sure how to get it working like the multiviews example.

Here is a screenshot for vsgmultirendergraphs:

This is expected (from vsgmultiviews):