tests/conform/texture-fbo: Log failure better
tests/conform/texture-fbo: Log failure better

We might as well print out exactly which assertion failed.

ebassi/clutter,djdeath/clutter,Distrotech/clutter,ebassi/clutter,djdeath/clutter,jigpu/clutter,jigpu/clutter,Distrotech/clutter,jigpu/clutter,GNOME/clutter,GNOME/clutter,djdeath/clutter,GNOME/clutter,GNOME/clutter,ebassi/clutter,djdeath/clutter,Distrotech/clutter,djdeath/clutter,Distrotech/clutter,jigpu/clutter,Distrotech/clutter,djdeath/clutter,Distrotech/clutter,jigpu/clutter,jigpu/clutter,GNOME/clutter,ebassi/clutter,ebassi/clutter