Add additional sink potion #dipping effects

Also put "Nothing seems to happen." into c_common_strings, since it's
used all over several files.

src/makemon.c

@@ -2422,7 +2422,7 @@ bagotricks(
                 update_inventory(); /* for perm_invent */
             }
         } else if (!tipping) {
-            pline1(!moncount ? nothing_happens : "Nothing seems to happen.");
+            pline1(!moncount ? nothing_happens : nothing_seems_to_happen);
         }
     }
     return moncount;