Part 2:

Moving the part of Sql_condition that contain condition items
(such as m_class_origin, m_cursor_name, etc) into a separate
class Sql_condition_items. This allows to remove duplicate code in
different Sql_condition constructors.

Also, introducing new Sql_condition constructors and removing the method
Sql_condition::set(). All code sequences that called an Sql_condition
constructor followed by Sql_condition::set() are now replaced to
the new constructor calls. This gives light performance improvement,
as the relevant members are now initialized only one time.