Redmine

Here is a patch where we use the headers.reverse_merge! method instead of headers.merge!

As we can pass headers as a parameter, I think we should use a reverse_merge in order to not override our hash with default values:

  def mail(headers={}, &block)
    headers.reverse_merge! 'X-Mailer' => 'Redmine',
            'X-Redmine-Host' => Setting.host_name,
            'X-Redmine-Site' => Setting.app_title,
            'X-Auto-Response-Suppress' => 'OOF',
            'Auto-Submitted' => 'auto-generated',
            'From' => Setting.mail_from,
            'List-Id' => "<#{Setting.mail_from.to_s.gsub('@', '.')}>" 

This could be very useful in some of my plugins. Thanks

Fix committed in r13784, thanks.