With big-league roster spots suddenly available, the Mets began the second half of the season tonight in Atlanta by adding AAA outfielder Prentice Redman and infielder Jorge Velandia to the roster. Redman looks to make his big-league debut in the No. 20 jersey recently left behind by Jeromy Burnitz; Velandia, who was up briefly in 2000 and 2001 wearing No. 11, is now wearing No. 13, which until last year looked like it might eventually have been retired for Edgardo Alfonzo. The Mets in the meantime may have seen the last of charismatic outfielder Tsuyoshi Shinjo 5, who was designated for assignment. Shinjo was banished to Norfolk late last month.