create_tmp_field_from_item() was creating tmp field without regard to
original field type of Item. This results in wrong type being reported to
client.

To create_tmp_field_from_item() added special handling for Items with 
DATE/TIME field types to preserve their type.


sql/sql_select.cc:
  Fix bug #11718 query with function, join and order by returns wrong type.
tests/mysql_client_test.c:
  Test case for bug #11718: query with function, join and order by returns wrong type