cogl: Use the GL_EXT_blend_{func,equation}_separate extensions
cogl: Use the GL_EXT_blend_{func,equation}_separate extensions

We should use these extensions to check for glBlendFuncSeparate and
glBlendEquationSeparate as well as checking the GL version number.

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