Restore support for 10.6 / i386

Hello,

I use an older Mac Mini as my media server, so I like to use VideoMonkey to transcode my media into something Apple-friendly.

These commits restore support for i386 and 10.6, but still build and run fine on 10.9.

The only part missing is building the utilities (e.g. ffmpeg) as fat binaries (i386 / x86_64) but I figured you had more experience doing that.

Note that this will use the OS-provided NSJSONSerialization if it is present (on 10.7 and up).

I also added a unit test bundle as well as a test class to show that my fixes work.

Thank you so much for creating and maintaining VideoMonkey!

Philippe Casgrain