header files for spi.h/trigger.h

   I am in the process of cleaning up the many un-needed includes and
   adding includes so each *.h file can is compile-able on its own.

Speaking of header files, I'm pretty sure that not enough header files
get installed in order to compile something using spi.h/trigger.h
outside the postgresql source tree.  This seems like a problem.

Shouldn't the normal install procedure install everything necessary to
use published postgresql header files?

Cheers,
Brook