triggers and C include files

In 31 Oct 2001 20:23 GMT source, doc/src/sgml/trigger.sgml mentions:

#include "executor/spi.h"   /* this is what you need to work with SPI */
#include "commands/trigger.h"   /* -"- and triggers */

for writing triggers in C, yet:

% cd src/include
% gmake -n install
/bin/sh ../../config/mkinstalldirs /usr/local/pgsql/include/libpq /usr/local/pgsql/include/internal/libpq
/usr/local/pgsql/include/internal/lib
for file in fmgr.h postgres.h access/attnum.h commands/trigger.h \       executor/spi.h utils/elog.h utils/geo_decls.h
utils/mcxt.h\       utils/palloc.h; do \       if cmp -s ./$file /usr/local/pgsql/include/$file; \       then \
     : ; \       else \               rm -f /usr/local/pgsql/include/$file; \       fi ; \
 
done
...


seems to actively want to get rid of those files (?!) Anyway, they are
definitely not installed on my system. So, have things changed and the
documentation lagged, or should those include files be installed?
(I have never written a C trigger function - yet.)

Cheers,

Patrick