Two changes:

1. if there are several symbols with the same entry number, sort those
   symbols in ASCII order.
2. Do not stop reading the header files when "BEGIN ERROR CODES" is
   found, since mkerr.pl will add a function declaration after that
   comment.  Instead, trigger on "Error codes for the \w+ function",
   which is the actual start of the error code macros.

Additionally, a few more debugging printouts that helped.