Bug #1064: SHOW CREATE TABLE: avoid allocations for simple tables, old client compatibility

sql/item.h:
  fixups
sql/sql_show.cc:
  avoid allocations for simple tables
  old client compatibility

sql/item.h

@@ -275,6 +275,7 @@ class Item_empty_string :public Item_string
 public:
   Item_empty_string(const char *header,uint length) :Item_string("",0)
     { name=(char*) header; max_length=length;}
+  void make_field(Send_field *field);
 };
 
 class Item_varbinary :public Item

sql/sql_show.cc

@@ -564,7 +564,8 @@ mysqld_show_create(THD *thd, TABLE_LIST *table_list)
     DBUG_RETURN(1);
   }
 
-  String packet;
+  char buff[1024];
+  String packet(buff,sizeof(buff));
   packet.length(0);
   net_store_data(&packet, table->table_name);
   /*
@@ -597,7 +598,8 @@ mysqld_show_create(THD *thd, TABLE_LIST *table_list)
 
   List<Item> field_list;
   field_list.push_back(new Item_empty_string("Table",NAME_LEN));
-  field_list.push_back(new Item_empty_string("Create Table",packet.length()));
+  field_list.push_back(new Item_empty_string("Create Table",
+        max(packet.length(),1024))); // 1024 is for not to confuse old clients
 
   if (send_fields(thd,field_list,1))
     DBUG_RETURN(1);