crashes mysqld": implementation for a generic item tree modifications
registry. Every item tree modification which should be rolled back for
subsequent execution of a prepared statement or stored procedure should
be saved in the registry. All such modifications are rolled back at once
during cleanup stage of PS.
Actual fix for the bug just adds a call to register modifications to
convert_constant_item.
Post review fixes implemented.


mysql-test/r/ps.result:
  A fix for bug#5748, test results fixed.
mysql-test/t/ps.test:
  A test case for Bug#5748 "Prepared statement with BETWEEN and bigint 
  values crashes mysqld"
sql/item.cc:
  Fix for Bug#5748 "Prepared statement with BETWEEN and bigint values
  crashes mysqld":
  First step in removing up item-specific cleanups: now all such
  tree modifications should be done using the genericm mechanism implemented
  in this changeset.
sql/item.h:
  Fix for Bug#5748 "Prepared statement with BETWEEN and bigint values
  crashes mysqld": no need for an item-specific change record any more.
sql/item_cmpfunc.cc:
  A fix for Bug#5748 "Prepared statement with BETWEEN and bigint 
  values crashes mysqld": register item tree transformation performed by
  convert_constant_item.
sql/sql_class.cc:
  Implementation for item tree transformations registry.
sql/sql_class.h:
  Declarations, necessary for the tree transformations registry.
sql/sql_parse.cc:
  Assert that the item tree transformations registry is not used for 
  conventional execution.
sql/sql_prepare.cc:
  Use of the item tree modifications registry in prepared statements:
  rollback all modifications in the end of statement prepare and execute.
  Also we now always set thd->current_arena to be able to determine that
  this is an execution of prepared statement inside the registry code.
tests/client_test.c:
  A typo fixed.