add browserify compatibility

index-browserify.js

+require("./d3.v2");
+module.exports = d3;
\ No newline at end of file

package.json

@@ -20,6 +20,7 @@
     "url": "http://github.com/mbostock/d3.git"
   },
   "main": "index.js",
+  "browserify" : "index-browserify.js",
   "dependencies": {
     "jsdom": "0.2.14",
     "sizzle": "1.1.x"