FullScreen.js was renamed to Fullscreen.js last night as part of a pull request I merged in from Scott. Because Windows is stupid, this will create minor problems for you when switching from a branch with the change to a branch without them. All you have to do is revert any changes to Fullscreen.js or FullscreenSpec.js that it thinks you made after checking out the branch. In either case, I suggest everyone merge master into your branch at your earliest convenience.
Matt