test-cogl-blend-strings: Add some more tests
test-cogl-blend-strings: Add some more tests

The adds tests for the remaining layer combine functions, the 1 minus
value operator and the TEXTURE_N source. Note however that Cogl
currently fails when parsing a TEXTURE_N source so the test is
commented out.

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