[No BUG#] Fixes for problems discovered when running mysql-trunk's subquery testsuite

sql/item.cc

@@ -6768,7 +6768,19 @@ my_decimal *Item_ref::val_decimal(my_decimal *decimal_value)
 int Item_ref::save_in_field(Field *to, bool no_conversions)
 {
   int res;
-  DBUG_ASSERT(!result_field);
+  if (result_field)
+  {
+    if (result_field->is_null())
+    {
+      null_value= 1;
+      res= set_field_to_null_with_conversions(to, no_conversions);
+      return res;
+    }
+    to->set_notnull();
+    res= field_conv(to, result_field);
+    null_value= 0;
+    return res;
+  }
   res= (*ref)->save_in_field(to, no_conversions);
   null_value= (*ref)->null_value;
   return res;

sql/opt_subselect.cc

@@ -1215,6 +1215,8 @@ static bool convert_subq_to_sj(JOIN *parent_join, Item_in_subselect *subq_pred)
   {
     tl->table->tablenr= table_no;
     tl->table->map= ((table_map)1) << table_no;
+    if (tl->is_jtbm())
+      tl->jtbm_table_no= tl->table->map;
     SELECT_LEX *old_sl= tl->select_lex;
     tl->select_lex= parent_join->select_lex; 
     for (TABLE_LIST *emb= tl->embedding;
@@ -3106,11 +3108,15 @@ bool setup_sj_materialization_part2(JOIN_TAB *sjm_tab)
       if (item_eq)
       {
         List_iterator<Item> it(item_eq->equal_items);
+        /* We're interested in field items only */
+        if (item_eq->get_const())
+          it++;
         Item *item;
         while ((item= it++))
         {
           if (!(item->used_tables() & ~emb_sj_nest->sj_inner_tables))
           {
+            DBUG_ASSERT(item->real_item()->type() == Item::FIELD_ITEM);
             copy_to= ((Item_field *) (item->real_item()))->field;
             break;
           }

sql/table.h

@@ -1766,6 +1766,7 @@ struct TABLE_LIST
    */
   char *get_table_name() { return view != NULL ? view_name.str : table_name; }
   bool is_active_sjm();
+  bool is_jtbm() { return test(jtbm_subselect!=NULL); }
   st_select_lex_unit *get_unit();
   st_select_lex *get_single_select();
   void wrap_into_nested_join(List<TABLE_LIST> &join_list);