Backport Assaf's recent ATI fix re point sprites to v1-6, but also generalise
Backport Assaf's recent ATI fix re point sprites to v1-6, but also generalise

--HG--
branch : v1-6

digimatic/ogre,digimatic/ogre,digimatic/ogre,digimatic/ogre,digimatic/ogre,digimatic/ogre,digimatic/ogre