Fence texture support on brush models, e.g. for rmqdemo2 e1m6rq.bsp. Based on Baker's implementation in Fitz Mark V. Consistent with Fitz Mark V, RMQEngine, FTEQW rendering.
Not implemented for world polys (afaik it's useless for world polys) but could be added if needed.

git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk@970 af15c1b1-3010-417e-b628-4374ebc0bcbd