Properly process duplicate RSS entries from Superfeedr

[maxh]

Apparently duplicate entries are part of the Superfeedr SLA:

http://blog.superfeedr.com/frequently-asked-questions.html

Duplicate entries/notifications : why do they happen?

We do all we can to avoid these, but you should make sure your app deals with them. As you know we use a very distributed architecture, which means that even our datastores are replicated. There is always a risk that replication to "too slow" sometimes, and that 2 parsers might run almost at the same time and see the same entry twice.

However, if you see recurring duplicate entries for a given feed, you may want to check that you haven't subscribed twice to this feed, with different endpoints. We send notifications for each {feed url | endpoint} pair.