Fix compilation error under gcc/linux.

src/nvimage/FloatImage.h

@@ -11,6 +11,7 @@
 
 namespace nv
 {
+class Vector4;
 class Matrix;
 class Image;
 class Filter;
@@ -63,7 +64,7 @@ public:
 	NVIMAGE_API void toGamma(uint base_component, uint num, float gamma = 2.2f);
 	NVIMAGE_API void exponentiate(uint base_component, uint num, float power);
 	
-	NVIMAGE_API void transform(uint base_component, const Matrix & m, Vector4::Arg offset);
+	NVIMAGE_API void transform(uint base_component, const Matrix & m, const Vector4 & offset);
 	NVIMAGE_API void swizzle(uint base_component, uint r, uint g, uint b, uint a);
 	
 	NVIMAGE_API FloatImage * fastDownSample() const;