code review from Josh and Robert

*** 22,41 ****
       anything at all.  For example, we could use an arena containing the
       integers minpid through maxpid to allocate process IDs.  For uses of this
       nature, prefer id_space(9F) instead.
  
       vmem_create() and vmem_destroy() create and destroy vmem arenas.  In
!      order to differentiate between arenas used for adresses and arenas used
       for identifiers, the VMC_IDENTIFIER flag is passed to vmem_create().
       This prevents identifier exhaustion from being diagnosed as general
       memory failure.
  
     Spans
       We represent the integers in an arena as a collection of spans, or
       contiguous ranges of integers.  For example, the kernel heap consists of
       just one span: [kernelheap, ekernelheap).  Spans can be added to an arena
!      in two ways: explicitly, by vmem_add(), or implicitly, by importing, as
       described in Imported Memory below.
  
     Segments
       Spans are subdivided into segments, each of which is either allocated or
       free.  A segment, like a span, is a contiguous range of integers.  Each
--- 22,41 ----
       anything at all.  For example, we could use an arena containing the
       integers minpid through maxpid to allocate process IDs.  For uses of this
       nature, prefer id_space(9F) instead.
  
       vmem_create() and vmem_destroy() create and destroy vmem arenas.  In
!      order to differentiate between arenas used for addresses and arenas used
       for identifiers, the VMC_IDENTIFIER flag is passed to vmem_create().
       This prevents identifier exhaustion from being diagnosed as general
       memory failure.
  
     Spans
       We represent the integers in an arena as a collection of spans, or
       contiguous ranges of integers.  For example, the kernel heap consists of
       just one span: [kernelheap, ekernelheap).  Spans can be added to an arena
!      in two ways: explicitly, by vmem_add(); or implicitly, by importing, as
       described in Imported Memory below.
  
     Segments
       Spans are subdivided into segments, each of which is either allocated or
       free.  A segment, like a span, is a contiguous range of integers.  Each