class copier :This engine copies data between file descriptors as specified by the
copy_task -> Unixqueue.event_system ->
The task is done when all input descriptors are at EOF. See
the description of
copy_task for details, especially whether
the descriptors are closed or not.
On error or abort, the descriptors are only closed if they had been closed on regular EOF.
The semantics of the engine is undefined if one of the descriptors is not stream-oriented.
TODO: This class cannot yet cope with Win32 named piped.