The last of the saving patches for d3dx9. :)
-- v3: d3dx9: Add support for saving IDirect3DVolumeTexture9 textures to DDS files in D3DXSaveTextureToFileInMemory(). d3dx9: Add support for saving IDirect3DCubeTexture9 textures to DDS files in D3DXSaveTextureToFileInMemory(). d3dx9: Add support for saving IDirect3DTexture9 textures to DDS files in D3DXSaveTextureToFileInMemory(). d3dx9/tests: Add more tests for saving textures to DDS files.