Comment 3 for bug 284596

Also, it's clearly said in ChangeLog:

2008-07-27 Dan Williams <email address hidden>
...
* src/connection-editor/main.c
                - Implement a single-app-instance object that exports a D-Bus API to
                        accept the same args that the connection editor does on the command
                        line
                - (main, try_existing_instance): if a connection editor is already open
                        in the current session, just send the command-line arguments to that
                        existing editor over D-Bus instead of spawning a second editor