Fixed a multimonitor issue.

If you have a monitor left of your primary one in X, the greeter it's positioning.

The fix was to also move the window to the x and y of the screen when updating the size.

This is what happens, pardon the crappy camera quality.
![nxgeayz](https://f.cloud.github.com/assets/68832/1412774/9dcf4bca-3deb-11e3-9153-de7bae80c76e.jpg)