fixup! PointInstancer : Add first-class PointInstancer type

Hopefully fixes linking errors on Windows.

Author: johnhaddon

include/IECoreScene/PointInstancer.h

@@ -117,7 +117,7 @@ class IECORESCENE_API PointInstancer : public IECoreScene::PointsPrimitive
 		///
 		/// Higher-level functionality used to evaluate the instancing.
 
-		struct VisibilityQuery
+		struct IECORESCENE_API VisibilityQuery
 		{
 
 			VisibilityQuery( const PointInstancer &pointInstancer )
@@ -143,7 +143,7 @@ class IECORESCENE_API PointInstancer : public IECoreScene::PointsPrimitive
 		};
 
 		/// Utility class to query properties for individual instances.
-		struct TransformQuery
+		struct IECORESCENE_API TransformQuery
 		{
 
 			TransformQuery( const PointInstancer &pointInstancer );