Catch 'address already in use' error when trying to use a port that is

in use by another program.  We now try to use a range of 40000-60000 
when this error occurs.

src/deluge_core.cpp

@@ -640,8 +640,14 @@ static PyObject *torrent_set_listen_on(PyObject *self, PyObject *args)
     if (!PyArg_ParseTuple(args, "O", &port_vec))
         return NULL;
 
+    try {
         M_ses->listen_on(std::make_pair( PyInt_AsLong(PyList_GetItem(port_vec, 0)),
             PyInt_AsLong(PyList_GetItem(port_vec, 1))), "");
+    }
+    catch (...) {
+        //Can't listen on that port, so lets try a range of 40000-60000
+        M_ses->listen_on(std::make_pair(40000, 60000), "");
+    }
 
     Py_INCREF(Py_None); return Py_None;
 }