LTRIM support for redis
LTRIM support for mongo
closes #1901
you're now logged out server-side when you're banned, so csrf token doesn't work in app.logout
closed #1910
closed #1850
#1375 part1
fix callback
one more fix
more fixes
removed debug
moved core notifications all the way to the end
closes #1911
reduced active users
get recent poster uids
mongodb list fix
cleaned up a bit
possible fix for #1909
optimize getPostSummaryByPids
optimize privileges and assorted fixes.

* new methods
privileges.categories.filter
privileges.topics.filter
privileges.posts.filter

they take a list of ids and a privilege, and return the filtered list of
ids, faster than doing  async.filter and calling the db for each id.

* remove event listeners on recent page before adding
* group.exists works for both single group names and arrays
* helpers.allowedTo works for both a single cid and an array of cids
* moved filter:topic.post hook right before topic creation.
* moved filter:topic.reply hook right before topic reply.