large refactoring, mostly to eliminate intermediate SigUp and provide a separate idle path
Merge branch 'master' of https://github.com/dmbarbour/Sirea
temporary for transfer to laptop (quite broken; in middle of changes to eliminate SigUp)
lots of sweeping changes; working towards more robust cycle processing; PCX now in IO; bfchoke now standard; removing implicit choke
finished propagating updates for changes in PCX and Lnk types.