Fixed $params for get_resource callback

Per @machuga's [post on Tumblr][1], there was a get_resource callback
which preloads resources in a before_filter allowing controller
methods to focus on view logic.

I find the $params in `_remap()` is actually router segments as
opposed to POST parameters as is in Rails.

[1]: http://machuga.tumblr.com/post/7181182435/codeigniter-filter-revisited