Prevent X11.app from launching & add Theme Name on OS X

Fix for issue #59, and check the value of `AppleAquaColorVariant` NSGlobalDomain for `Win_theme` value, and return `Graphite` or `Blue`. 
![screen shot 2013-10-22 at 4 12 33 pm](https://f.cloud.github.com/assets/491458/1379868/24aaa760-3afa-11e3-9d32-24589dceda43.png)