dvec.h, add a pointer to the original vector to dvec structure

src/frontend/vectors.c

@@ -720,6 +720,7 @@ vec_copy(struct dvec *v)
     nv->v_next = NULL;
     nv->v_link2 = NULL;
     nv->v_scale = v->v_scale;
+	nv->v_unclipped = v->v_unclipped;
 
     return (nv);
 }

src/include/ngspice/dvec.h

@@ -58,6 +58,7 @@ struct dvec {
     struct dvec *v_next;	/* Link for list of plot vectors. */
     struct dvec *v_link2;	/* Extra link for things like print. */
     struct dvec *v_scale;	/* If this has a non-standard scale... */
+    struct dvec *v_unclipped;	/* If clipped, this is the original vector */
 } ;
 
 #define isreal(v)   ((v)->v_flags & VF_REAL)