Add dummy structure for passing redirections

Implementation coming soon.
Implement fd passing throught UNIX socket.

An additional socket is added to pass fds.
Remove an unused FILE
Implement output redirection

* The interface will change to allow redirection of arbitrary fd
* dasc now redirects all outputs to /dev/null
Remove dummy input redirection code
Server: remove unused TubeFd
Server: tube variable names cleanup
Server: Remove unused TubeFd