Use approximate sin/cos for faster interpolation.

This particular approximation is taken from
<http://www.devmaster.net/forums/showthread.php?t=5784> but there may well be
better ones out there.  This seems to work nicely though!

examples/bundle/bundle-radial.js

@@ -8,16 +8,37 @@ var cluster = d3.layout.cluster()
 
 var bundle = d3.layout.bundle();
 
+// From http://www.devmaster.net/forums/showthread.php?t=5784
+function sin(x) {
+  if (x > Math.PI) x -= 2 * Math.PI;
+  var B = 4 / Math.PI,
+      C = -4 / (Math.PI * Math.PI),
+
+      y = B * x + C * x * Math.abs(x);
+
+  //#ifdef EXTRA_PRECISION
+    var Q = 0.775,
+        P = 0.225;
+
+    y = P * (y * Math.abs(y) - y) + y;   // Q * y + P * y * abs(y)
+  //#endif
+  return y;
+}
+
+function cos(x) {
+  return sin(x + Math.PI / 2);
+}
+
 var line = d3.svg.line()
     .interpolate("basis")
     .beta(.85)
     .x(function(d) {
       var r = d.y, a = (d.x - 90) / 180 * Math.PI;
-      return r * Math.cos(a);
+      return r * cos(a);
     })
     .y(function(d) {
       var r = d.y, a = (d.x - 90) / 180 * Math.PI;
-      return r * Math.sin(a);
+      return r * sin(a);
     });
 
 var vis = d3.select("#chart").append("svg:svg")