Stop double escaping params

What has been happening is that URL-encoded params that have an escapable character in them (like a forward-slash) are already escaped by the time they get here, and then the percent symbol `%` is re-escaped.

No bueno.

In my case, I am trying to pass a parameter `type=text/plain`. The `text/plain` portion gets escaped to `text%2Fplain`, but then gets re-escaped to `text%252Fplain`.