    KMain()
      includes ::/StartOS.HC
        includes ~/MakeHome.HC
          includes ~/HomeSys.HC
            calls StartUpTasks()
              includes ~/Once.HC
                calls OnceExe().

    AOnce() appends src code to ~/Registry.HC Once/Adam tree, executed at next boot
    by Adam.

    Once()  appends src code to ~/Registry.HC Once/User tree, executed at next boot
    by first User term.

    At boot, OnceExe(), executes Once/Adam tree, AOnceFlush()s it,
    executes Once/User tree and OnceFlush()s.