adds nocase query to wrap value in case insensitive regex

[adamclerk]

I was having problems getting ?location_regex=/boise/i to work so I created a custom querystring class nocase.

[baugarten]

I dislike that it would be exposed as ?location_nocase and location_regex=/boise/i

I'm in the middle of a rewrite, in which filters underwent a major refactory. I think it'll be easier to add it in there. If you're interested in contributing, check out origin/rewrite -- I'll be accepting PR's on that branch