Cleanup of doc files.

Fixed xterm.py (and cleanup) to clean up screen sessions.
Cleaned up sshd.py (though interface is still in flux.)
Added 1024-node network example (treenet1024.py).
Added example showing multiple tests on a single network (multitest.py).
Renamed examples to make them easier to type!

examples/treenet1024.py

@@ -0,0 +1,15 @@
+#!/usr/bin/python
+
+"""
+Create a 1024-host network, and run the CLI on it.
+If this fails because of kernel limits, you may have
+to adjust them, e.g. by adding entries to /etc/sysctl.conf
+and running sysctl -p.
+"""
+   
+from mininet import init, TreeNet
+
+if __name__ == '__main__':
+   init()
+   network = TreeNet( depth=2, fanout=32, kernel=True )
+   network.run( Cli )