Added IndexBufferAttribute. Woops!

src/core/IndexBufferAttribute.js

@@ -0,0 +1,12 @@
+/**
+ * @author mrdoob / http://mrdoob.com/
+ */
+
+THREE.IndexBufferAttribute = function ( array, itemSize ) {
+
+	THREE.BufferAttribute.call( this, array, itemSize );
+
+};
+
+THREE.IndexBufferAttribute.prototype = Object.create( THREE.BufferAttribute.prototype );
+THREE.IndexBufferAttribute.prototype.constructor = THREE.IndexBufferAttribute;