Add support for X-XSS-Protection header.

Add support for X-XSS-Protection header.

Although it's only useful for older IE browsers (IE8), it's still an important feature.  It's still used in the wild today.  You see Twitter, Facebook, and Google have it.  We will enable this by default.

# MEOWWWW 
![LOL](http://i.imgur.com/TBjRSKy.gif)