celeron55/minetest — pull request #314 by dannydark (2012-11-28 19:17:48+00:00)
Title: Add the ability to check if image exists

This patch by celeron55 (see discussion here: http://irc.minetest.ru/minetest-dev/2012-11-28#i_2668712) adds isKnownSourceImage to TextureSource which
lets us check if a image exists or not.

Example: With my textured crosshair branch it lets us check if the image exists and if not we fall back to the old style crosshair instead of just creating a dummy image.