add a sinkhole email backend

It makes all mails sent by Django go to an unique recipient; use it on
development and preproduction platforms when there are productions
accounts loaded.

entrouvert/djommon/email_backends/sinkhole.py

@@ -0,0 +1,25 @@
+from django.conf import settings
+
+from django.core.mail.backends.smtp import EmailBackend as SmtpEmailBackend
+from django.core.mail.message import sanitize_address
+from django.utils.encoding import force_bytes
+
+class EmailBackend(SmtpEmailBackend):
+    def _send(self, email_message):
+        """A helper method that does the actual sending."""
+        if not email_message.recipients():
+            return False
+        from_email = sanitize_address(email_message.from_email,
+                email_message.encoding)
+        recipients = [ settings.EMAIL_SINK_RECIPIENT ]
+        message = email_message.message()
+        charset = message.get_charset().get_output_charset() if message.get_charset() else 'utf-8'
+        try:
+            self.connection.sendmail(from_email, recipients,
+                    force_bytes(message.as_string(), charset))
+        except:
+            if not self.fail_silently:
+                raise
+            return False
+        return True
+