startup of second instance of coccinella without warning/exception

Attached patch allows startup of coccinella on the same host for a second time, without the second instance whining about already used ports for the built-in server and http server.
On startup it now checks, whether the port configured in the preferences is in use, if not, then its just used. Otherwise the port number is counted up once, and tried again. In case its needed, this is done for 500 times before coccinella gives up to find an unused port.

The File transfer port for the whiteboard is somehow differently handled, therefore its not considered in this patch (yet). This port is also not opened on startup, only later when a file transfer is started...

In case the user needs to know the port used, he can check which port was used in the preferences.

This would aid me in developing/debugging things on a single machine, i.e. having a jabber server and two clients running on my notebook.

Sander what do you think about this patch?