How to determine (in a port Makefile) if KSE is present?

[Darren Pilgrim]

I have a port which uses a static-linked 5.4 binary.  This is broken in 
8.0 due to KSE removal.  I need to create a test and limit installation 
to only those versions on which it will run.

Looking at the heads-up message for KSE removal from March 2008, I don't 
see a change to sys/sys/param.h, so I don't think __FreeBSD_version was 
bumped.  Looking at the commit log for param.h and lining up timestamps, 
I think 800024 would be the last version with KSE support.

Is it therefore prudent to allow install only if 504000 <= OSVERSION <= 
800024 or should I test for KSE another way?