Use forward declaration to reduce build times.

components/sceneutil/shadow.cpp

@@ -9,6 +9,8 @@
 
 #include <components/settings/settings.hpp>
 
+#include "mwshadowtechnique.hpp"
+
 namespace SceneUtil
 {
     using namespace osgShadow;

components/sceneutil/shadow.hpp

@@ -7,10 +7,10 @@
 #include <components/terrain/quadtreeworld.hpp>
 #include <components/shader/shadermanager.hpp>
 
-#include "mwshadowtechnique.hpp"
-
 namespace SceneUtil
 {
+    class MWShadowTechnique;
+
     class ShadowManager
     {
     public: