Ah my bad, didn't thought of the backwards compatibility, with my current commits it will cause error both ways. What I can think of now is to put the singleton mechanism inside the `construct` method:

		public function __construct() {

			if (is_null(self::$instance))
				self::$instance =& $this;
			else
				return;

So we don't called it with `TGM_Plugin_Activation::instance()`, but still the same way `new TGM_Plugin_Activation`.

This way, if the older version of TGMPA loaded first, there won't be any error, but there is nothing we can't do about the multiplied number of notices issue. If the newer version loaded first, there won't be any error and the issue will gone. What do you think?