function detectTypeSupport( type, typeUri ) {
		// based on Modernizr's lossless img-webp test
		// note: asynchronous
		var image = new window.Image();
		image.onerror = function() {
			types[ type ] = false;
			picturefill();
		};
		image.onload = function() {
			types[ type ] = image.width === 1;
			picturefill();
		};
		image.src = typeUri;
		return "pending";
	}
outputs a warning for the developer
@param {message}
@type {Function}