Fix bz175: Pile mark is shown when potion is destroyed

Original bug report:

> When killing something that's carrying a potion, or death-drops a potion,
> or stands on top of a potion, with a force bolt or a wand of striking,
> "you hear something shatter" or "a potion of foo shatters" but the corpse
> is inverse as if it's (still) a pile.

Unfortunately the newsym() checks for already existing glyph, and
the gbuf doesn't distinguish between object piles and single items,
so newsym doesn't mark the location for update.

This is a dirty hack to force the newsym to update the glyph.
The glyph buffering should be revisited in a future version.

include/extern.h

@@ -310,6 +310,7 @@ E void FDECL(map_location, (int, int, int));
 E void FDECL(feel_newsym, (XCHAR_P, XCHAR_P));
 E void FDECL(feel_location, (XCHAR_P, XCHAR_P));
 E void FDECL(newsym, (int, int));
+E void FDECL(newsym_force, (int, int));
 E void FDECL(shieldeff, (XCHAR_P, XCHAR_P));
 E void FDECL(tmp_at, (int, int));
 E void FDECL(swallowed, (int));

src/display.c

@@ -1318,6 +1318,21 @@ static gbuf_entry gbuf[ROWNO][COLNO];
 static char gbuf_start[ROWNO];
 static char gbuf_stop[ROWNO];
 
+/* FIXME: This is a dirty hack, because newsym() doesn't distinguish
+ * between object piles and single objects, it doesn't mark the location
+ * for update. */
+void
+newsym_force(x, y)
+register int x, y;
+{
+    newsym(x,y);
+    gbuf[y][x].new = 1;
+    if (gbuf_start[y] > x)
+        gbuf_start[y] = x;
+    if (gbuf_stop[y] < x)
+        gbuf_stop[y] = x;
+}
+
 /*
  * Store the glyph in the 3rd screen for later flushing.
  */

src/zap.c

@@ -1875,10 +1875,14 @@ struct obj *obj, *otmp;
                         You_hear("a crumbling sound.");
                 }
             } else {
+                int oox = obj->ox;
+                int ooy = obj->oy;
                 if (context.mon_moving
                         ? !breaks(obj, obj->ox, obj->oy)
                         : !hero_breaks(obj, obj->ox, obj->oy, FALSE))
                     maybelearnit = FALSE; /* nothing broke */
+                else
+                    newsym_force(oox,ooy);
                 res = 0;
             }
             if (maybelearnit)