fs.createWriteStream throws fs undefined error

The improved test suite now catches this bug, so hopefully thing like
this will not happen again.

See: http://github.com/ry/node/issues#issue/75

lib/fs.js

@@ -1,6 +1,7 @@
 var
   sys = require('sys'),
-  events = require('events');
+  events = require('events'),
+  fs = require('fs');
 
 exports.Stats = process.Stats;