Fixing issues whilst building under node 0.10

This fixes a change in API in node 0.10 described on the wiki: 

https://github.com/joyent/node/wiki/Api-changes-between-v0.8-and-v0.10

"The `uv_after_work_cb` signature has changed to take a second integer argument
 indicating status. For backwards compatibility, explicitly cast the 4th 
argument to `uv_queue_work`"