tcpip: fixed bug in circular buffer.

We have to keep track of the number of data-bytes separately.
Otherwise we might make wrong decisions by e.g. thinking that
data is available, although it's actually just a control packet.
tcpip: fixed type-errors that occurred on x86_64.
tcpip: improved print-function of circular buffer.
tcpip: improved logging.
Changed cleanpath() to not add a trailing slash.
Changed stdio functions to be more consistent.

So, now we have simply multiple ways to create a FILE
object and the rest is the same.
ls: sort case insensitive.
shell: allow '@'.
Added open(fd) to fstream.
tcpip: continue to receive data even when closing.

At least, it's required to ACK the data we continue to receive.
tcpip: use the same seqNo when resending control packets.
tcpip: send FIN|ACK when closing.
Added /mnt.
Added a simple FTP filesystem.

It is currently readonly and has some other limitations,
but it seems to work fine.
Fixes and improvements for fstream.

- don't free and reallocate the buffer when using open().
- ignore exceptions when closing (destructor...)
- don't flush the buffer if our state is bad
tcpip: only call replyRead if the pending is request is a read.
tcpip: check for already pending requests in connect.
ftpfs: reconnect if our connection broke.
ftpfs: added write-support.
tcpip: fixed issues if sending more than receiver's win-size.