Define globals and add semicolons to wp-fullscreen.js.

`grunt jshint` now runs clean for WordPress core!

props mattwiebe.
fixes #26029.

Built from https://develop.svn.wordpress.org/trunk@26667


git-svn-id: http://core.svn.wordpress.org/trunk@26557 1a063a9b-81f0-0310-95a4-ce76da25c4cd