Fix PathTraversal to leave encoding of PATH_INFO unchanged

In current implementation, PathTraversal#cleanup method changes encoding of `env['PATH_INFO']` to `US-ASCII` (script default encoding) from `ASCII-8BIT` on Ruby 1.9.x.  (Ruby 2.0+ is safe)
Because `US-ASCII` is not 8bit clean, that behavior breaks some modules (such as [http_router](https://github.com/joshbuddy/http_router) ) when we access URLs with non-latin characters.

So I wrote the patch encoding in Ruby 1.9+ aware.

Also dayflower@7875ec5 commit is attached to this pull-request, in which escape chars in captals (eg. `%2E`) avoidance is fixed.