A fix for proxy issues when mixing '/' and '%2F' in URIs.

CornerCouch tends to produce URIs with `%2F`, e.g.` /database/_design%2Fapp`, and this causes certain problems with proxies and URL rewrites which fail to match URL against rules with `/` chars. For example, simplest CouchDB proxy using node.js http-proxy module will expose this problem.

With this pull request I'm adding minimal and "brute-force" solution: replace all `%2F` with `/` in URIs, and this solves all problems on my local server.