Faster compilation speed

[David S. Miller]

   From: "Timothy J. Wood" <tjw@omnigroup.com>
   Date: Wed, 14 Aug 2002 11:27:07 -0700
   
      You can easily use much less than a full word.  Foundation on 
   OpenStep/Mach 4.2 started storing partial ref counts in whatever spare 
   bits were available in each object.

We don't have any spare bits, we have 32 bits used for RTX state then
the next object is a pointer.  So whatever size counter we use will
eat at a minimum a word's worth of space to get the pointers aligned
up properly.