systat - clarify 'Free' in systat -vm 1

systat - clarify 'Free' in systat -vm 1

* Clarify Free by indicating i+c+f (inactive + cache + free).  That is,
  the Free memory reported in the upper left counts the Inactive page
  queue as part of its total, even though it isn't quite free.

* The main reason for this is that when the memory pressure de-stresses,
  the VM system doesn't bother wasting time moving pages out of the inactive
  queue, even though they are effectively freeable.

  On the otherhand, if the system is under significant memory pressure,
  the inactive queue will itself become stressed and minimize.

  This makes it a fairly accurate representation of what is potentially
  freeable (albeit with some effort by the paging system).