. Replace some hardwired /usr/X11R6 instances with X11BASE. 
. Replace some hardwired /usr/local instances with LOCALBASE.
. Small Makefile restructure to keep related variables in one place.
. Add ipv6 to CATEGORIES if its enabled. 
PR: 106130 
Submitted by: Janos Mohacsi <email@example.com> 
Pointed out by: pointyhat (via kris)