filter to prevent multiple occurences of the same station in a coinciden...

If the same station occurs more tan once in a coincidence, it can happen that the same station acts twice in a triple for direction reconstruction. This leads to ' division by zero'  error (because phi1 = phi 2). To change is to prevent this error. A consequence of the change is that the single coincidence with more than once the same station is replaced by more than one coincidences with a station occuring only once in each coincidence.