Strong params

o/

First of all. I'm aware you guys are not keen on non fast forward merges. The reason I'm trying this PR is only an attempt to improve the workflow for upgrading Rails 4 since I myself am pretty much interested at helping on that.

I believe this will be a slow incremental change and merging ``master`` into ``strong_params``, or whatever is the name for Rails 4 for upgrade branch, every once in a while, maybe once a week, is the best way to go. Letting ``master`` too far away from this branch should lead to an extremely painful and highly error prone merge/rebase. And since Rails 4 will be some day in Spree master I believe it makes sense to merge master into strong_params every once in a while.

I think this approach also helps the community to contribute more easily on the upgrade. Rebasing will confuse users every time they try to update their local repo, guess this happened already on 95a75e927349652410b474a581f53f04e11c79b0. Other than that @radar could merge patches into ``strong_params`` the same way he likes to do on all the other branchs, revise pull and amend as he pleases.

ps. It's been a while I want to take a closer look into Rails 4 and I think this is an awesome opportunity. I'd post to see your thoughts on spree-user group but I figured I'd better just starting it myself in case you approve the idea.