Check if running in iframe-async mode and adapt
Check if running in iframe-async mode and adapt

To avoid blocking onload, we'd like boomerang to run in an iframe-async
mode.  This is described in detail by Stoyan here:
  http://www.phpied.com/non-onload-blocking-async-js/

Also check the references on that article.

We have a few complications because we need access to the parent window
object, need to make our API available to callers in the parent window,
and as far as possible need to load before the document's onload event
fires.  This requires us to define the BOOMR object on the parent as
well as the current window.

lognormal/boomerang,lognormal/boomerang