[HECnet] Use of Area 63 for Testing

There's nothing special about area number 63 in the architecture, or in PyDECnet -- nor, as far as I know, in any other DECnet implementation. The "hidden area" idea was used within DEC, since the Engineering Net at some point outgrew the 16 bit address space. I don't really remember anymore how it was used. I can try to construct some schemes that would work; the one I just constructed in my head is rather messy and I don't know if it is correct. A possible answer relies on using max areas = 62 in most of the network, but = 63 in the routers that connect to hidden area entry points. The other complication is that we'd have to resurrect the PMR / PASSTHRU object. There's a PDP-10 version that's been posted, but my Macro-10 is much too feeble these days to read it. I don't have the RSTS version, but I may have code that talks to it which may be sufficient. Given a decent spec of how it works, a Python version would be easy. paul