Begin d3 v4 update

modules/util/rebind.js

@@ -0,0 +1,16 @@
+// Copies a variable number of methods from source to target.
+export function rebind(target, source) {
+  var i = 1, n = arguments.length, method;
+  while (++i < n) target[method = arguments[i]] = d3_rebind(target, source, source[method]);
+  return target;
+};
+
+// Method is assumed to be a standard D3 getter-setter:
+// If passed with no arguments, gets the value.
+// If passed with arguments, sets the value and returns the target.
+function d3_rebind(target, source, method) {
+  return function() {
+    var value = method.apply(source, arguments);
+    return value === source ? target : value;
+  };
+}