fails:IO.copy_stream from an IO to an IO starts writing at the destination IO's current position
fails:IO.copy_stream from a file name to an IO starts writing at the destination IO's current position
fails:IO.copy_stream from a pipe IO raises an error when an offset is specified
fails:IO.copy_stream from a pipe IO to an IO starts writing at the destination IO's current position
fails:IO.copy_stream with non-IO Objects calls #readpartial on the source Object if defined
