Cycles Hair: add Generated texture coordinates for curves, so that procedural
textures now work without having to add a UV map.

Also made UV and intercept attributes only export when needed by the shader.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53529 954f8c5b-7b00-dc11-b283-0030488c597c