[PATCH] pgarchives: bugfix: increase listsubscription username length

The listsubscription username field is populated by pglister_sync,
copying information from auth_user.email, which can be up to
254 characters.
If a user defined an email address that is longer than 30
characters, pglister_sync will crash:

Traceback (most recent call last):
   File "/path/pglister_sync.py", line 83, in <module>
     curs.execute("WITH t(u) AS (SELECT UNNEST(%(usernames)s::text[])), ins(un) AS (INSERT INTO listsubscribers
(username,list_id) SELECT u, %(listid)s FROM t WHERE NOT EXISTS (SELECT 1 FROM listsubscribers WHERE username=u AND
list_id=%(listid)s)RETURNING username), del(un) AS (DELETE FROM listsubscribers WHERE list_id=%(listid)s AND NOT EXISTS
(SELECT1 FROM t WHERE u=username) RETURNING username) SELECT 'ins',un FROM ins UNION ALL SELECT 'del',un FROM del ORDER
BY1,2", {
 
psycopg2.errors.StringDataRightTruncation: value too long for type character varying(30)

This patch fixes the issue by using the same max length as any
django email field for this field.
-- 
Célestin Matte