Submissions/Comments by subreddit per user

For @atiaxi and all who wish to review, the query cache is new territory for me.

Allows for filtering content by subreddit on your own profile page (or if you are an admin).  Only works on new sort.

In the future I would like to expose this to moderators, so that they may see what a user has contributed to in their own subreddits.

Sadly the dropdown list only shows subreddits in which your content has been voted as it uses the sr karmas list to get the subreddits.  I assumed it was added and set to value at submission time, however, it appears to not be.  Account.has_interacted_with() also uses this list...

Do query caches will have to be updated for existing users?  How does that usually work?