Aliased function exports are broken #648

In a situation like this...

var CubeGeometry;
CubeGeometry = BoxGeometry;

function BoxGeometry ( options ) {
    /* code goes here */
};

export { CubeGeometry, BoxGeometry };

...the BoxGeometry function becomes function exports.BoxGeometry which is obviously broken. Interestingly if you initialise CubeGeometry immediately it works fine.