error for LIMIT placeholder".
The patch adds grammar support for LIMIT ?, ? and changes the
type of ST_SELECT_LEX::select_limit,offset_limit from ha_rows to Item*,
so that it can point to Item_param.


mysql-test/include/ps_modify.inc:
  Fix existing tests: now LIMIT can contain placeholders.
mysql-test/include/ps_query.inc:
  Fix existing tests: now LIMIT can contain placeholders.
mysql-test/r/ps.result:
  Add basic test coverage for LIMIT ?, ? and fix test results.
mysql-test/r/ps_2myisam.result:
  Fix test results: now LIMIT can contain placeholders.
mysql-test/r/ps_3innodb.result:
  Fix test results: now LIMIT can contain placeholders.
mysql-test/r/ps_4heap.result:
  Fix test results: now LIMIT can contain placeholders.
mysql-test/r/ps_5merge.result:
  Fix test results: now LIMIT can contain placeholders.
mysql-test/r/ps_6bdb.result:
  Fix test results: now LIMIT can contain placeholders.
mysql-test/r/ps_7ndb.result:
  Fix test results: now LIMIT can contain placeholders.
mysql-test/t/ps.test:
  Add basic test coverage for LIMIT ?, ?.
sql/item.h:
  Add a short-cut for (ulonglong) val_int() to Item.
  Add a constructor to Item_int() that accepts ulonglong.
  Simplify Item_uint constructor by using the c-tor above.
sql/item_subselect.cc:
  Now select_limit has type Item *.
  We can safely create an Item in Item_exists_subselect::fix_length_and_dec():
  it will be allocated in runtime memory root and freed in the end of
  execution.
sql/sp_head.cc:
  Add a special initalization state for stored procedures to 
  be able to easily distinguish the first execution of a stored procedure
  from prepared statement prepare.
sql/sql_class.h:
  Introduce new state 'INITIALIZED_FOR_SP' to be able to easily distinguish
  the first execution of a stored procedure from prepared statement prepare.
sql/sql_derived.cc:
  - use unit->set_limit() to set unit->select_limit_cnt, offset_limit_cnt
    evreryplace. Add a warning about use of set_limit in 
  mysql_derived_filling.
sql/sql_error.cc:
  - use unit->set_limit() to set unit->select_limit_cnt, offset_limit_cnt
    evreryplace.
  - this change is also aware of bug#11095 "show warnings limit 0 returns 
  all rows instead of zero rows", so the one who merges the bugfix from
  4.1 can use local version of sql_error.cc.
sql/sql_handler.cc:
  - use unit->set_limit() to initalize 
  unit->select_limit_cnt,offset_limit_cnt everyplace.
sql/sql_lex.cc:
  Now ST_SELECT_LEX::select_limit, offset_limit have type Item *
sql/sql_lex.h:
  Now ST_SELECT_LEX::select_limit, offset_limit have type Item *
sql/sql_parse.cc:
  - use unit->set_limit() to initalize 
  unit->select_limit_cnt,offset_limit_cnt everyplace. 
  - we can create an Item_int to set global limit of a statement:
  it will be created in the runtime mem root and freed in the end of
  execution.
sql/sql_repl.cc:
  Use unit->set_limit to initialize limits.
sql/sql_select.cc:
  - select_limit is now Item* so the proper way to check for default value
  is to compare it with NULL.
sql/sql_union.cc:
  Evaluate offset_limit_cnt using the new type of ST_SELECT_LEX::offset_limit
sql/sql_view.cc:
  Now ST_SELECT_LEX::select_limit, offset_limit have type Item *
sql/sql_yacc.yy:
  Add grammar support for LIMIT ?, ? clause.