Note: bug#21726 does not directly apply to 4.1, as it doesn't have stored
procedures.  However, 4.1 had some bugs that were fixed in 5.0 by the
patch for bug#21726, and this patch is a backport of those fixes.
Namely, in 4.1 it fixes:

  - LAST_INSERT_ID(expr) didn't return value of expr (4.1 specific).

  - LAST_INSERT_ID() could return the value generated by current
    statement if the call happens after the generation, like in

      CREATE TABLE t1 (i INT AUTO_INCREMENT PRIMARY KEY, j INT);
      INSERT INTO t1 VALUES (NULL, 0), (NULL, LAST_INSERT_ID());

  - Redundant binary log LAST_INSERT_ID_EVENTs could be generated.


mysql-test/r/rpl_insert_id.result:
  Add result for bug#21726: Incorrect result with multiple invocations
  of LAST_INSERT_ID.
mysql-test/t/rpl_insert_id.test:
  Add test case for bug#21726: Incorrect result with multiple invocations
  of LAST_INSERT_ID.
sql/item_func.cc:
  Add implementation of Item_func_last_insert_id::fix_fields(), where we
  set THD::last_insert_id_used when statement calls LAST_INSERT_ID().
  In Item_func_last_insert_id::val_int(), return THD::current_insert_id
  if called like LAST_INSERT_ID(), otherwise return value of argument if
  called like LAST_INSERT_ID(expr).
sql/item_func.h:
  Add declaration of Item_func_last_insert_id::fix_fields().
sql/log_event.cc:
  Do not set THD::last_insert_id_used on LAST_INSERT_ID_EVENT.  Though we
  know the statement will call LAST_INSERT_ID(), it wasn't called yet.
sql/set_var.cc:
  In sys_var_last_insert_id::value_ptr(), set THD::last_insert_id_used,
  and return THD::current_insert_id for @@LAST_INSERT_ID.
sql/sql_class.h:
  Update comments.
  Remove THD::insert_id(), as it has lost its purpose now.
sql/sql_insert.cc:
  Now it is OK to read THD::last_insert_id directly.
sql/sql_load.cc:
  Now it is OK to read THD::last_insert_id directly.
sql/sql_parse.cc:
  In mysql_execute_command(), remember THD::last_insert_id (first
  generated value of the previous statement) in THD::current_insert_id,
  which then will be returned for LAST_INSERT_ID() and @@LAST_INSERT_ID.
sql/sql_select.cc:
  If "IS NULL" is replaced with "= <LAST_INSERT_ID>", use right value,
  which is THD::current_insert_id, and also set THD::last_insert_id_used
  to issue binary log LAST_INSERT_ID_EVENT.
sql/sql_update.cc:
  Now it is OK to read THD::last_insert_id directly.
tests/mysql_client_test.c:
  Add test case for bug#21726: Incorrect result with multiple invocations
  of LAST_INSERT_ID.