Add ExternalInterface API to determine if audio has been recorded (jGetAudioLength?)

[shanplourde]

One limitation of the Flash component at this time is that it's impossible to determine on the client side via JavaScript if the Flash recorder contains in-memory recorded audio. It would be useful to expose an API via ExternalInterface such as jGetAudioLength or something similar that would simply return the number of bytes consumed by the current recorded audio. This would allow JavaScript validations to take place before attempting to perform an HTTP POST.

[shanplourde]

Obviously it would be great if the HTTP response status were included in the callback as well