cad/brlcad: Sanitize MANPREFIX

cad/brlcad/Makefile

@@ -33,7 +33,7 @@ TEST_TARGET=	check
 
 CONFLICTS_INSTALL=	py[23][0-9]-epsilon
 
-MANPREFIX=	${PREFIX}/${PORTNAME}/share
+MANDIRS=	${PREFIX}/${PORTNAME}/share/man
 NO_MTREE=	yes
 
 WRKSRC=${WRKDIR}/${PORTNAME}-${PORTVERSION}