fix issue #1061 - dipping container into water

Issue reported by loggersviii:  dipping a container into an uncursed
potion of water mentions water getting into the container.  That
happens even when that type of potion hasn't been discovered yet.

Make POT_WATER become discovered if this occurs.  Doesn't apply when
hallucinating where a random liquid is mentioned instead of water.

Fixes #1061

src/potion.c

@@ -1512,8 +1512,12 @@ H2Opotion_dip(
     } else {
         /* dipping into uncursed water; carried() check skips steed saddle */
         if (carried(targobj)) {
+            gm.mentioned_water = FALSE; /* water_damage() might set this */
             if (water_damage(targobj, 0, TRUE) != ER_NOTHING)
                 res = TRUE;
+            if (gm.mentioned_water)
+                makeknown(POT_WATER);
+            gm.mentioned_water = FALSE;
         }
     }
     if (func) {