add Emacs.app back to the bottle

The actual code change involved is just bumping the version to 24.2-boxen2. This is so boxen will install a new bottle that was built with `--cocoa --srgb`. That bottle can be found [here](http://files.bleything.net/emacs-24.2-boxen2.tar.bz2).

One thing I wasn't sure about: I wanted to add the build options to the manifest so if the bottle doesn't exist it gets built properly, but I wasn't entirely sure how. I'd be happy to add another commit if you can guide me.