use forward declarations for better namespace hygiene

src/VORONOI/compute_voronoi_atom.cpp

@@ -19,6 +19,7 @@
 #include <cmath>
 #include <cstring>
 #include <cstdlib>
+#include "voro++.hh"
 #include "compute_voronoi_atom.h"
 #include "atom.h"
 #include "group.h"

src/VORONOI/compute_voronoi_atom.h

@@ -21,7 +21,12 @@ ComputeStyle(voronoi/atom,ComputeVoronoi)
 #define LMP_COMPUTE_VORONOI_H
 
 #include "compute.h"
-#include "voro++.hh"
+
+namespace voro {
+  class container;
+  class container_poly;
+  class voronoicell_neighbor;
+}
 
 namespace LAMMPS_NS {