ftpfs: fixed bugs in generation of dir entries.
Fixed error-number in ClientDevice::joinshm.
tcpip: MSS is given in big endian.
tcpip: ensure that we don't resend data if we don't want to.

We only want to resend the data after a timeout. When we've got
a packet, we might want to send additional data, but not the same
again. Note that the problem did only occur if we got a "weird"
ACK. For example, if we got an ACK for the stuff before the data
we've just sent, then we would've sent the data again, without
reason.
ftpfs: use File{Read,Write} for response.
ftpfs: use ABOR if we want to stop reading.

Sending a RST over the data-connection does not suffice. We need
to tell the server over the control-connection that we want to
stop.
It's a bit tricky to do that because if the transfer is still in
progress, we'll get just the response for ABOR. If it's already
finished, we get the response for the transfer, too. That means,
we have to know when a transfer is complete. To do so, I use the
size of the file from the directory listing.