[FIX] mail: forum reply shows as 'False'

When posting a comment after an answer in the forum, a mail
was sent to each subscriber with 'Re: False' as title.

In fact the title has to be 'Re:' + the name of the parent
record of this message.

When a mail is sent from the post, a link to access the subject
of the forum must be included in the mail.

opw:679073

addons/mail/data/mail_data.xml

@@ -69,7 +69,7 @@
         <meta itemprop="name" content="View ${ctx['model_name']}"/>
     </div>
 </div>
-% if not ctx['is_discussion'] or not len(ctx['actions']) == 0:
+% if not ctx['is_discussion'] or not len(ctx['actions']) == 0 or ctx.get('is_accessible'):
 <div summary="o_mail_notification" style="padding:0px; width:600px; margin:0 auto; background: #FFFFFF repeat top /100%;color:#777777">
     <table cellspacing="0" cellpadding="0" style="width:600px; border-collapse:collapse; background:inherit; color:inherit">
         <tbody><tr>

addons/mail/models/mail_thread.py

@@ -1814,6 +1814,9 @@ class MailThread(models.AbstractModel):
         for x in ('from', 'to', 'cc'):
             values.pop(x, None)
 
+        if not values['subject'] and self._name == 'forum.post':
+            values['record_name'] = self.parent_id and self.parent_id.name
+
         # Post the message
         new_message = MailMessage.create(values)
 

addons/mail/models/res_partner.py

@@ -74,6 +74,7 @@ class Partner(models.Model):
                              tracking_value.get_new_display_value()[0]))
 
         is_discussion = message.subtype_id.id == self.env['ir.model.data'].xmlid_to_res_id('mail.mt_comment')
+        is_accessible = message.model == "forum.post"
 
         return {
             'signature': signature,
@@ -83,6 +84,7 @@ class Partner(models.Model):
             'record_name': record_name,
             'tracking': tracking,
             'is_discussion': is_discussion,
+            'is_accessible': is_accessible
         }
 
     @api.model