cogl-clip-stack: Fix flushing multiple stencil rectangles
cogl-clip-stack: Fix flushing multiple stencil rectangles

When flushing a clip stack that contains more than one rectangle which
needs to use the stencil buffer the code takes a different path so
that it can combine the new rectangle with the existing contents of
the stencil buffer. However it was not correctly flushing the
modelview and projection matrices so that rectangle would be in the
wrong place.

collects/clutter,Distrotech/clutter,nobled/clutter,kerrickstaley/clutter-vala,Distrotech/clutter,djdeath/clutter-android,kerrickstaley/clutter-vala,djdeath/clutter-android,djdeath/clutter,djdeath/clutter-android,djdeath/clutter,kerrickstaley/clutter-vala,kerrickstaley/clutter-vala,heysion/clutter-clone,Distrotech/clutter,GNOME/clutter,heysion/clutter-clone,djdeath/clutter,ebassi/clutter,dlespiau/clutter,djdeath/clutter-android,djdeath/clutter-multithreaded,GNOME/clutter,Distrotech/clutter,spatulasnout/clutter,heysion/clutter-clone,spatulasnout/clutter,ebassi/clutter,jigpu/clutter,collects/clutter,collects/clutter,dlespiau/clutter,heysion/clutter-clone,nobled/clutter,GNOME/clutter,dlespiau/clutter,ebassi/clutter,collects/clutter,spatulasnout/clutter,djdeath/clutter-multithreaded,djdeath/clutter,jigpu/clutter,Distrotech/clutter,nobled/clutter,Distrotech/clutter,spatulasnout/clutter,heysion/clutter-clone,ebassi/clutter,spatulasnout/clutter,GNOME/clutter,djdeath/clutter-multithreaded,djdeath/clutter,jigpu/clutter,jigpu/clutter,ebassi/clutter,djdeath/clutter-android,collects/clutter,jigpu/clutter,jigpu/clutter,djdeath/clutter,djdeath/clutter-multithreaded,GNOME/clutter