Needing the version string of a dependancy

[Paul Ripke <stix%stix.id.au@localhost>]

I've been fixing up wip/nlopt. math/octave is an optional dependency,
and if selected, PLIST needs the octave version string. How is this
normally done? Hunting around, it seems the way this is normally done
is to reference an exported var, exported from buildlink3.mk, eg.
SCIVERSION from math/scilab.

Is this the recommendation? Should something like this export be done
by default?

-- 
Paul Ripke
"Great minds discuss ideas, average minds discuss events, small minds
 discuss people."
-- Disputed: Often attributed to Eleanor Roosevelt. 1948.