Fix issue #294 (really this time).

Add stencil attachment to framebuffer creation. Needed to remove depth
attachment to make it work, but that should not change anything, since depth
test is not enabled anyway. May need testing nonetheless.

src/modules/graphics/opengl/wrap_Graphics.cpp

@@ -169,9 +169,6 @@ namespace opengl
 
 	static int setStencil(lua_State * L, bool invert)
 	{
-		// stencils require the default fb to work properly
-		Canvas::TemporaryUnbinder unbinder;
-
 		// no argument -> clear mask
 		if (lua_isnoneornil(L, 1)) {
 			instance->discardStencil();