fix more python 2.6 related bugs

cartero/utils/sending.py

@@ -60,7 +60,7 @@ class CampaignDeliver(object):
             if href and href.startswith('http'):
                 short_url, created = ShortURL.objects.get_or_create(url=href)
                 url = reverse('click_monitor', args=[short_url.code, self.campaign.id])
-                fqdn_url = 'http://{}{}'.format(self.site.domain, url)
+                fqdn_url = 'http://{0}{1}'.format(self.site.domain, url)
                 link.attrib['href'] = fqdn_url
         return tree
 
@@ -70,7 +70,7 @@ class CampaignDeliver(object):
         mail_track = MailTracks(campaign=self.campaign, contact=contact)
         mail_track.save()
         url = reverse('track', args=[mail_track.id,])
-        fqdn_image_url = 'http://{}{}'.format(self.site.domain, url)
+        fqdn_image_url = 'http://{0}{1}'.format(self.site.domain, url)
         img.attrib['src'] = fqdn_image_url
         return tree
 
@@ -97,7 +97,7 @@ class CampaignDeliver(object):
                 'last_name': contact.last_name,
                 'email': contact.email,
                 'site': contact.site,
-                'unsubscribe_url': 'http://{}{}'.format(contact.site.domain, unsubscribe_url),
+                'unsubscribe_url': 'http://{0}{1}'.format(contact.site.domain, unsubscribe_url),
                 }
         if contact.data:
             data = json.loads(contact.data)