Unbreak maintenance/deleteDefaultMessages.php for PostgreSQL

Unbreak maintenance/deleteDefaultMessages.php for PostgreSQL

deleteDefaultMessages.php was failing during upgrade
from MediaWiki 1.7.3 with a databaser error.

A stub user:

   $user = User::newFromName( 'MediaWiki default' );

has user ID 0, so that $user->isAnon() is true.

Unfortunately, ManualLogEntry::publish() from r96441
tries to insert $user->getName() ("MediaWiki default")
into rc_ip.

PostgreSQL won't allow this, because rc_ip is of
Postgres-specific CIDR type.

Traceback:

Checking existence of old default messages...
...deleting old default messages (this may take a long time!)...A database query syntax error has occurred.
The last attempted database query was:
"INSERT INTO "recentchanges" (rc_timestamp,rc_cur_time,rc_namespace,rc_title,rc_type,rc_minor,rc_user,rc_user_text,rc_comment,rc_this_oldid,rc_last_oldid,rc_bot,rc_moved_to_ns,rc_moved_to_title,rc_ip,rc_patrolled,rc_new,rc_old_len,rc_new_len,rc_deleted,rc_logid,rc_log_type,rc_log_action,rc_params,rc_id) VALUES ('2012-03-14 21:51:05 GMT','2012-03-14 21:51:05 GMT','8','1movedto2','3','0','0','MediaWiki default','No longer required','0','0',1,'0','','MediaWiki default','1','0',NULL,NULL,'0','1','delete','delete','a:0:{}','1')"
from within function "RecentChange::save".
MySQL returned error "1: ERROR:  invalid input syntax for type cidr: "MediaWiki default"
LINE 1: ...ki default','No longer required','0','0',1,'0','','MediaWiki...
                                                             ^"
Backtrace:
#0 /usr/home/saper/public_html/pg/w/includes/db/DatabasePostgres.php(332): DatabaseBase->reportQueryError('ERROR:  invalid...', 1, 'INSERT INTO "re...', 'RecentChange::s...', '')
#1 /usr/home/saper/public_html/pg/w/includes/db/Database.php(904): DatabasePostgres->reportQueryError('ERROR:  invalid...', 1, 'INSERT INTO "re...', 'RecentChange::s...', '')
#2 /usr/home/saper/public_html/pg/w/includes/db/DatabasePostgres.php(604): DatabaseBase->query('INSERT INTO "re...', 'RecentChange::s...', '')
#3 /usr/home/saper/public_html/pg/w/includes/RecentChange.php(199): DatabasePostgres->insert('recentchanges', Array, 'RecentChange::s...')
#4 /usr/home/saper/public_html/pg/w/includes/logging/LogEntry.php(479): RecentChange->save('pleasedontudp')
#5 /usr/home/saper/public_html/pg/w/includes/WikiPage.php(2042): ManualLogEntry->publish('1')
#6 /usr/home/saper/public_html/pg/w/includes/WikiPage.php(1937): WikiPage->doDeleteArticleReal('No longer requi...', false, 0, false, '', Object(User))
#7 /usr/home/saper/public_html/pg/w/maintenance/deleteDefaultMessages.php(73): WikiPage->doDeleteArticle('No longer requi...', false, 0, false, '', Object(User))
#8 /usr/home/saper/public_html/pg/w/maintenance/update.php(128): DeleteDefaultMessages->execute()
#9 /usr/home/saper/public_html/pg/w/maintenance/doMaintenance.php(105): UpdateMediaWiki->execute()
#10 /usr/home/saper/public_html/pg/w/maintenance/update.php(151): require_once('/usr/home/saper...')
#11 {main}