tests: Display the index inside text-box-layout
tests: Display the index inside text-box-layout

Since the rectangles packed inside the BoxLayout interactive test
have random colors it's not easy to verify the ordering. By using
the CoglPango API to print out the index in the middle of each
rectangle.

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