Creating a DateTime from UTC seconds
===

I can't believe that I can't find this anywhere, but how can you create a DateTime from UTC seconds? Similar to how in Java you can do `Calendar.getInstance().setTimeInMillis(time)` to get a certain time.

`DateTime.new 1344899588` didn't work, and I don't see anything in the DateTime API docs that shows how to do this.

This works, but seems like a roundabout way to do it:

    DateTime.strptime(1344899588.to_s, "%s")