bots filter should include more bots
A common bot that seems to crawl redmine is:
"Sogou web spider/4.0(+http://www.sogou.com/docs/help/webmasters.htm#07)"
but it is not listed as one of the known bots in bots_filter.rb
Actually, there are quite a large number of other bots that aren't listed. It might be good to add a much larger list from the internet, or be more smart about adding them dynamically.