Add missing include found by greenya

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@3601 dfc29bdd-3216-0410-991c-e03cc46cb475

include/irrlicht.h

@@ -129,6 +129,7 @@
 #include "path.h"
 #include "irrXML.h"
 #include "ISceneCollisionManager.h"
+#include "ISceneLoader.h"
 #include "ISceneManager.h"
 #include "ISceneNode.h"
 #include "ISceneNodeAnimator.h"