Merge in 1.3 and post 1.3 fixes; some of them might be applicable to

other ppp ports.

- XXX: we don't check for the exact version of new features added, so
  this might not compile for all post 1.3 versions. It should be trivial
  to fix.

- ppp can delay the last packet so check:
	    && (sc->sc_if.if_snd.ifq_head || sc->sc_fastq.ifq_head
		|| sc->sc_outm)) {
  instead of just:
	    && (sc->sc_if.if_snd.ifq_head || sc->sc_fastq.ifq_head)) {

- glue in ipflow fast forwarding.

- Only run pppasyncstart (sc->sc_start) from the netisr handler.
  This allows pppoutput to be called from splimp (e.g., when ipflow is
  in use.) without requiring pppasyncstart to run at splimp.

- defopt INET, NETATALK

- Remove force argument to pppstart; it is not necessary anymore.