Forgot to include these files in sculpt shape key commit.

source/blender/blenkernel/BKE_key.h

@@ -60,6 +60,7 @@ float *do_ob_key(struct Scene *scene, struct Object *ob);
 
 struct Key *ob_get_key(struct Object *ob);
 struct KeyBlock *ob_get_keyblock(struct Object *ob);
+struct KeyBlock *ob_get_reference_keyblock(struct Object *ob);
 struct KeyBlock *key_get_keyblock(struct Key *key, int index);
 struct KeyBlock *key_get_named_keyblock(struct Key *key, const char name[]);
 char *key_get_curValue_rnaPath(struct Key *key, struct KeyBlock *kb);

source/blender/blenkernel/BKE_paint.h

@@ -68,6 +68,9 @@ typedef struct SculptSession {
 	struct MFace *mface;
 	int totvert, totface;
 	float *face_normals;
+
+	struct Object *ob;
+	struct KeyBlock *kb, *refkb;
 	
 	/* Mesh connectivity */
 	struct ListBase *fmap;

source/blender/blenkernel/intern/key.c

@@ -1408,6 +1408,16 @@ KeyBlock *ob_get_keyblock(Object *ob)
 	return NULL;
 }
 
+KeyBlock *ob_get_reference_keyblock(Object *ob)
+{
+	Key *key= ob_get_key(ob);
+	
+	if (key)
+		return key->refkey;
+
+	return NULL;
+}
+
 /* get the appropriate KeyBlock given an index */
 KeyBlock *key_get_keyblock(Key *key, int index)
 {