[6.1] write in mail.message fails because of non existing variable in fetchmail overriding function

When calling mail_message.send, the call fails because fetchmail.py overrides the mail_message.write function with a function containing a not existing variable.

Error in log:
  File "/home/openeyedev/var/openerp/addons_6.1/mail/mail_message.py", line 502, in send
    self.write(cr, uid, ids, {'state': 'outgoing'}, context=context)
NameError: global name 'server_id' is not defined

These kind of errors should never happen if modern IDE's were used that would catch these errors immediately.

Anyway below is the failing part of the code:

    def write(self, cr, uid, ids, values, context=None):
        if context is None:
            context={}
        fetchmail_server_id = context.get('fetchmail_server_id')
        if fetchmail_server_id:
            values['fetchmail_server_id'] = server_id
        res = super(mail_message,self).write(cr, uid, ids, values, context=context)
        return res

The variable server_id in the third line from below does not exist. it should be fetchmail_server_id.

This has been fixed in trunk / 7.0 in revision r8037, but left unchanged in 6.1.