Replaced non standard Precedence email header with "X-Auto-Response-Suppress: OOF" (#9534).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@7805 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/mailer.rb

@@ -378,7 +378,7 @@ class Mailer < ActionMailer::Base
     headers 'X-Mailer' => 'Redmine',
             'X-Redmine-Host' => Setting.host_name,
             'X-Redmine-Site' => Setting.app_title,
-            'Precedence' => 'bulk',
+            'X-Auto-Response-Suppress' => 'OOF',
             'Auto-Submitted' => 'auto-generated'
   end