> extern char         *   sys_errlist[];
> extern char         *   sys_siglist[];

You should comment out/delete these and use the system includes.

> If I comment this line is popper.h out everything compiles fine but
> strange behaviour is the result...

What strange behavior?  It's unlikely that the above declarations are
causing it, whatever it may be.

-allen

-- 
Allen Briggs - end killing - allen.briggs@bev.net ** MacBSD == NetBSD/mac68k **
   Where does all my time go?  <a href="http://www.netbsd.org/">Guess.</a>