Bugfix: stdin fd (0) being ignored by node.File.

In the case of stdin options.fd is 0, which is considered false, therefore fd
gets set to null intead of 0.
http://groups.google.com/group/nodejs/msg/80849f6aa0b0eaa0

src/file.js

@@ -52,7 +52,7 @@ node.fs.File = function (options) {
     self.encoding = node.RAW;
   }
   //node.debug("encoding: opts=" + options.encoding + " self=" + self.encoding);
-  self.fd = options.fd || null;
+  self.fd = typeof options.fd != 'undefined' ? options.fd : null;
 
   var actionQueue = [];