o Redesign the layering mechanism and make the aliasing code part of

o Redesign the layering mechanism and make the aliasing code part of
  the layering.

  We now ``stack'' layers as soon as we open the device (when we figure
  out what we're dealing with).  A static set of `dispatch' routines are
  also declared for dealing with incoming packets after they've been
  `pulled' up through the stacked layers.

  Physical devices are now assigned handlers based on the device type
  when they're opened.  For the moment there are three device types;
  ttys, execs and tcps.

o Increment version number to 2.2
o Make an entry in [uw]tmp for non-tty -direct invocations (after
  pap/chap authentication).
o Make throughput counters quad_t's
o Account for the absolute number of mbuf malloc()s and free()s in
  ``show mem''.
o ``show modem'' becomes ``show physical''.