NDB table".

SQL-layer was not marking fields which were used in triggers as such. As
result these fields were not always properly retrieved/stored by handler
layer. So one might got wrong values or lost changes in triggers for NDB,
Federated and possibly InnoDB tables.
This fix solves the problem by marking fields used in triggers
appropriately.

Also this patch contains the following cleanup of ha_ndbcluster code:

We no longer rely on reading LEX::sql_command value in handler in order
to determine if we can enable optimization which allows us to handle REPLACE
statement in more efficient way by doing replaces directly in write_row()
method without reporting error to SQL-layer.
Instead we rely on SQL-layer informing us whether this optimization
applicable by calling handler::extra() method with
HA_EXTRA_WRITE_CAN_REPLACE flag.
As result we no longer apply this optimzation in cases when it should not
be used (e.g. if we have on delete triggers on table) and use in some
additional cases when it is applicable (e.g. for LOAD DATA REPLACE).

Finally this patch includes fix for bug#20728 "REPLACE does not work
correctly for NDB table with PK and unique index".
  
This was yet another problem which was caused by improper field mark-up.
During row replacement fields which weren't explicity used in REPLACE
statement were not marked as fields to be saved (updated) so they have
retained values from old row version. The fix is to mark all table
fields as set for REPLACE statement. Note that in 5.1 we already solve
this problem by notifying handler that it should save values from all
fields only in case when real replacement happens.


include/my_base.h:
  Added HA_EXTRA_WRITE_CAN_REPLACE, HA_EXTRA_WRITE_CANNOT_REPLACE - new
  parameters for ha_extra() method. We use them to inform handler that
  write_row() which tries to insert new row into the table and encounters
  some already existing row with same primary/unique key can replace old
  row with new row instead of reporting error.
mysql-test/r/federated.result:
  Additional test for bug#18437 "Wrong values inserted with a before update
  trigger on NDB table".
mysql-test/r/ndb_replace.result:
  Added test for bug #20728 "REPLACE does not work correctly for NDB table
  with PK and unique index". Updated wrong results from older test.
mysql-test/t/federated.test:
  Additional test for bug#18437 "Wrong values inserted with a before update
  trigger on NDB table".
mysql-test/t/ndb_replace.test:
  Added test for bug #20728 "REPLACE does not work correctly for NDB table
  with PK and unique index".
sql/ha_ndbcluster.cc:
  We no longer rely on reading LEX::sql_command value in handler in order
  to determine if we can enable optimization which allows us to handle REPLACE
  statement in more efficient way by doing replaces directly in write_row()
  method without reporting error to SQL-layer.
  Instead we rely on SQL-layer informing us whether this optimization
  applicable by calling handler::extra() method with
  HA_EXTRA_WRITE_CAN_REPLACE flag.
  As result we no longer apply this optimization in cases when it should not
  be used (e.g. if we have on delete triggers on table) and use in some
  additional cases when it is applicable (e.g. for LOAD DATA REPLACE).
sql/item.cc:
  Item_trigger_field::setup_field():
    Added comment explaining why we don't set Field::query_id in this method.
sql/mysql_priv.h:
  mysql_alter_table() function no longer takes handle_duplicates argument.
  Added declaration of mark_fields_used_by_triggers_for_insert_stmt() function.
sql/sql_delete.cc:
  Mark fields which are used by ON DELETE triggers so handler will retrieve
  values for these fields.
sql/sql_insert.cc:
  Explicitly inform handler that we are doing REPLACE (using ha_extra() method)
  in cases when it can promote insert operation done by write_row() to replace.
  Also when we do REPLACE we want to store values for all columns so we should
  inform handler about it.
  Finally we should mark fields used by ON UPDATE/ON DELETE triggers as such
  so handler can properly retrieve/restore values in these fields during
  execution of REPLACE and INSERT ... ON DUPLICATE KEY UPDATE statements.
sql/sql_load.cc:
  Explicitly inform handler that we are doing LOAD DATA REPLACE (using
  ha_extra() method) in cases when it can promote insert operation done by
  write_row() to replace.
  Also when we do replace we want to save (replace) values for all columns
  so we should inform handler about it.
  Finally to properly execute LOAD DATA for table with triggers we should
  mark fields used by ON INSERT triggers as such so handler can properly
  store values for these fields.
sql/sql_parse.cc:
  mysql_alter_table() function no longer takes handle_duplicates argument.
sql/sql_table.cc:
  Got rid of handle_duplicates argument in mysql_alter_table() and
  copy_data_between_tables() functions. These functions were always
  called with handle_duplicates == DUP_ERROR and thus contained dead
  (and probably incorrect) code.
sql/sql_trigger.cc:
  Added Table_triggers_list::mark_fields_used() method which is used to mark
  fields read/set by triggers as such so handlers will be able properly
  retrieve/store values in these fields.
sql/sql_trigger.h:
  Table_triggers_list:
    Added mark_fields_used() method which is used to mark fields read/set by
    triggers as such so handlers will be able properly retrieve/store values
    in these fields. To implement this method added 'trigger_fields' member
    which is array of lists linking items for all fields used in triggers
    grouped by event and action time.
sql/sql_update.cc:
  Mark fields which are used by ON UPDATE triggers so handler will retrieve
  and save values for these fields.
mysql-test/r/ndb_trigger.result:
  Added test for bug#18437 "Wrong values inserted with a before update trigger
  on NDB table".
mysql-test/t/ndb_trigger.test:
  Added test for bug#18437 "Wrong values inserted with a before update trigger
  on NDB table".