Detail (debugging aid)

When compiling with option HARDMEMTESTS, every creation of a new key
in a table forces an emergency GC.

ltable.c

@@ -910,6 +910,8 @@ static void luaH_newkey (lua_State *L, Table *t, const TValue *key,
       newcheckedkey(t, key, value);  /* insert key in grown table */
     }
     luaC_barrierback(L, obj2gco(t), key);
+    /* for debugging only: any new key may force an emergency collection */
+    condchangemem(L, (void)0, (void)0, 1);
   }
 }