Some old crap which nobody needs and which probably nobody uses.
This relies on a GCC extension: using "## __VA_ARGS__" to remove the
comma from the argument list if the va args are empty. It's supported
by clang, and there's some chance newer standards will introduce a
proper way to do this. (Even if it breaks somewhere, it will be a
problem only for 1 release, since I want to drop the deprecated
properties immediately.)