Disable z buffer writes on shadows, can only help. Does not fix skidlines being behind wheels, however

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@14354 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/graphics/shadow.cpp

@@ -29,6 +29,7 @@ Shadow::Shadow(video::ITexture *texture, scene::ISceneNode *node, float scale =
     m.setTexture(0, texture);
     m.BackfaceCulling = false;
     m.MaterialType = video::EMT_TRANSPARENT_ALPHA_CHANNEL;
+    m.setFlag(video::EMF_ZWRITE_ENABLE , false);
     m_mesh   = irr_driver->createQuadMesh(&m, /*create_one_quad*/true);
     scene::IMeshBuffer *buffer = m_mesh->getMeshBuffer(0);
     irr::video::S3DVertex* v=(video::S3DVertex*)buffer->getVertices();