Notes on how to maintain 16/32 bit single source code.

We use the macros (message crackers etc) in port1632.h - which means:

In the 16 bit environment
  The header files
    port1632.h
      ptypes16.h
      pwin16.h
      plan16.h
  must all be visible and WIN16 must be defined.

In the 32 bit environment
  The header files
    port1632.h
      ptypes32.h
      pcrt32.h
      pwin32.h
      plan16.h
  must all be visible and WIN32 must be defined.