#507 - Fixed incorrect number of unread notifications.

The bug was caused because by setting the counts to whatever value we
were incrementing by, rather then using the values returned from Redis.

I've added a testcase which stresses notification incrementing with
2 activities that don't get aggregated.
Merge branch 'issue-507-notificationsUnreadCount' of git://github.com/simong/Hilary into issue-507-notificationsUnreadCount
Updating docs