Fixed segfault due to window being garbage collected prematurely.
* window.close() must be called to properly clean up resources.
* Bumped Contextify to 0.0.3.
Switch to Contextify to manage the window's script execution.
FIX: Asynchronous callbacks (such as timers) now execute in window
context. test/jsdom/index.js:timer_executes_in_context now passes.
FIX: Memory leaks from where context was never freed.