[Merge] lp:~kai-mast/friends/keep-mentions into lp:friends

[Robert Bruce Park]

Hi Kai, I have a couple concerns about this branch:

* I'd like to see the 'counts' dict be a defaultdict. Then you save having to check whether the stream is already present or not. 

* I see a lot of deletions from the testsuite and no additions. Any way you can flesh out the tests to cover the new behavior?
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https://code.launchpad.net/~kai-mast/friends/keep-mentions/+merge/204784
Your team Super Friends is requested to review the proposed merge of lp:~kai-mast/friends/keep-mentions into lp:friends.