OSX defaults wants a type.... sometimes

I was having issues with osx_defaults not setting certain variables and having them actually stick, especially boolean values. This adds the option to set a type along with the other values. If the option isn't set, it works as before.

Example:

    boxen::osx_defaults { "Disable 'natural scrolling'":
      key    => 'com.apple.swipescrolldirection',
      domain => 'NSGlobalDomain',
      value  => 'false',
      type   => 'bool',
    }

As soon as I added this, they started working. Maybe it's strictly related to Mountain Lion, but i'm not entirely sure.

Thanks for the great work so far!