graphics/kgraphviewer: fix build

- Boost was previously pulled in implicitly by KDE Frameworks;
  make it an explicit build-dep.

graphics/kgraphviewer/Makefile

@@ -1,6 +1,6 @@
 PORTNAME=	kgraphviewer
 DISTVERSION=	2.4.3
-PORTREVISION=	4
+PORTREVISION=	5
 CATEGORIES=	graphics kde
 MASTER_SITES=   KDE/stable/${PORTNAME}/${PORTVERSION}/
 DIST_SUBDIR=    KDE/${PORTNAME}
@@ -11,6 +11,7 @@ COMMENT=	Graphs-viewer for GraphViz files
 LICENSE=	GPLv2
 LICENSE_FILE=	${WRKSRC}/COPYING
 
+BUILD_DEPENDS=	${LOCALBASE}/include/boost/concept_check.hpp:devel/boost-libs
 LIB_DEPENDS=	libgvc.so:graphics/graphviz
 
 USES=		cmake compiler:c++11-lang desktop-file-utils kde:5 qt:5 tar:xz \