This is quite an old thread now (just recently brought back from the mists of time by that parrot fellow) and I think that we may have gone further into that somewhere or other; can't recall at this time of night whether it was here or in another thread. Could well be worth revisiting some points and tying up some loose ends, though, and I at least know a fair bit more than I did four years ago when the question was first asked. Tomorrow, maybe.