#2 Server mode

[Alexander Koller]

If started in server mode, utool should wait for socket
connections on a user-specified port. Once a connection
is established, it reads one-line messages from the
socket. Each line is expected to be an XML element that
specifies the command. Then the result is computed and
sent back as an XML element.<p>

An example for an XML message to the server could be

<code>
&lt;solve input-codec="domcon-oz"
output-codec="domcon-oz"&gt; blah blah blah (constraint
in domcon-oz format will be CDATA) &lt;/solve&gt;
</code>

The server-mode utool should support all commands and
codecs that the command-line utool accepts as commands
on the command line.