getFile callback called more than once

I am seeing an odd behaviour where the callback is being fired more than once. This happens when the getFile request produces an 'Error: read ECONNRESET'. I've ran this multiple times and I get the same behaviour. I have also asked a question about it on stack overflow that has more detailed information about it. It is [here](http://stackoverflow.com/questions/36989824/async-retry-callback-already-called)

Start at the getFile entry point and reproduce the reported Error: read ECONNRESET case, using the linked Stack Overflow discussion for the detailed scenario. Trace the error path and callback invocations; done means the callback fires exactly once when this request fails.

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