Shuffle before enclose.

Fixes d3#83.

src/array.js

@@ -0,0 +1,17 @@
+export var slice = Array.prototype.slice;
+
+export function shuffle(array) {
+  var m = array.length,
+      i0 = 0,
+      t,
+      i;
+
+  while (m) {
+    i = Math.random() * m-- | 0;
+    t = array[m + i0];
+    array[m + i0] = array[i + i0];
+    array[i + i0] = t;
+  }
+
+  return array;
+}

src/pack/enclose.js

@@ -1,5 +1,7 @@
+import {shuffle, slice} from "../array";
+
 export default function(circles) {
-  var i = 0, n = circles.length, B = [], p, e;
+  var i = 0, n = (circles = shuffle(slice.call(circles))).length, B = [], p, e;
 
   while (i < n) {
     p = circles[i];