For the post that got the most number of answers owned by csgillespie, how many answers did it get?
"csgillespie" is the DisplayName of user; the most number of answer refers to Max(AnswerCount)
SELECT MAX(T1.AnswerCount) FROM posts AS T1 INNER JOIN users AS T2 ON T1.OwnerUserId = T2.Id WHERE T2.DisplayName = 'csgillespie'