remove curse vs saddle

Prayer reward can already uncurse a cursed saddle because hero is
stuck on it.  Allow scroll/spell of remove curse to do so too.

The original riding implementation in slash'em operated with the
saddle in hero's inventory rather than in the steed's, so it would
have handled this without any extra effort.  Presumeably that was
overlooked when incorporating riding into nethack changed it to
have saddle be part of the steed's inventory instead of hero's.

src/potion.c

@@ -1214,12 +1214,13 @@ bottlename(void)
 
 /* handle item dipped into water potion or steed saddle splashed by same */
 static boolean
-H2Opotion_dip(struct obj *potion, struct obj *targobj,
-              boolean useeit,
-              const char *objphrase) /* "Your widget glows" or "Steed's saddle
-                                        glows" */
+H2Opotion_dip(struct obj *potion,    /* water */
+              struct obj *targobj,   /* item being dipped into the water */
+              boolean useeit,        /* will hero see the glow/aura? */
+              const char *objphrase) /* "Your widget glows" or
+                                      * "Steed's saddle glows" */
 {
-    void (*func)(OBJ_P) = 0;
+    void (*func)(struct obj *) = 0;
     const char *glowcolor = 0;
 #define COST_alter (-2)
 #define COST_none (-1)