Set the size of the extents used to hold pages in a Queue database,
specified as a number of pages. Each extent is created as a separate
physical file. If no extent size is set, the default behavior is to
create only a single underlying database file.
The Db::set_q_extentsize interface may only be used to configure Berkeley DB before
the Db::open interface is called.
The Db::set_q_extentsize method either returns a non-zero error value or throws an exception that
encapsulates a non-zero error value on failure, and returns 0 on success.