Adds iOS and Windows implementation; mention in the docs
Adds corresponding tests
Increases spec.35 timeout for Windows Phone 8.1 case as it contains 2 download operations
Increases timeout for Windows case for spec.10, spec.21 (abort right away), spec.15 (unknown host)
Documents the latency quirk caused by BackgroundDownloader usage
[Windows] Mark an upload aborted to be cancelled right away as it did not have enough time to be created when abort was called in filetransfer.spec.21 (so that unexpected httpWin fired)
Extended test buffer to avoid unexpectedCallbacks.httpWin on Windows & local test server (filetransfer.spec.21)
daserge