Handle operations which complete without being at the start of the queue
Move towards "invalidated" as terminology
Cancelling the whole queue does the job
Expose the enqueued file operations
Cancel in a very boring manner
Protect against ops in the queue which have already started
Changed my mind; don't expose -isCancelled after all
OK, uploader itself can't reach a "cancelled" state
Handle there being no completion handler
Handle operation not being in the queue
There's no point handing cancellation errors to the delegate to decide over