Patch by Michael Pruett: make regen work on Irix 6.0 and 6.5.

Lib/plat-irix6/regen

 #! /bin/sh
 case `uname -sr` in
-'IRIX '[45].*)	;;
+'IRIX '[456].*)	;;
+'IRIX64 '[456].*)	;;
 *)	echo Probably not on an IRIX system 1>&2
 	exit 1;;
 esac