fixed SET with subselect

mysql-test/r/subselect.result:
  test of SET with subselect
mysql-test/t/subselect.test:
  test of SET with subselect

mysql-test/r/subselect.result

@@ -848,6 +848,13 @@ do @a:=(SELECT a from t);
 select @a;
 @a
 1
+set @a:=2;
+set @a:=(SELECT a from t);
+select @a;
+@a
+1
 drop table t;
 do (SELECT a from t);
 Table 'test.t' doesn't exist
+set @a:=(SELECT a from t);
+Table 'test.t' doesn't exist

mysql-test/t/subselect.test

@@ -468,6 +468,11 @@ create table t (a int);
 insert into t values (1);
 do @a:=(SELECT a from t);
 select @a;
+set @a:=2;
+set @a:=(SELECT a from t);
+select @a;
 drop table t;
 -- error 1146
 do (SELECT a from t);
+-- error 1146
+set @a:=(SELECT a from t);
\ No newline at end of file

sql/sql_parse.cc

@@ -2470,9 +2470,16 @@ mysql_execute_command(THD *thd)
     break;
   }
   case SQLCOM_SET_OPTION:
-    if (!(res=sql_set_variables(thd, &lex->var_list)))
+    if (tables && ((res= check_table_access(thd, SELECT_ACL, tables)) ||
+		   (res= open_and_lock_tables(thd,tables))))
+      break;
+    fix_tables_pointers(lex->all_selects_list);
+    if (!(res= sql_set_variables(thd, &lex->var_list)))
       send_ok(thd);
+    if (thd->net.report_error)
+      res= -1;
     break;
+
   case SQLCOM_UNLOCK_TABLES:
     unlock_locked_tables(thd);
     if (thd->options & OPTION_TABLE_LOCK)