URLs can't contain utf-8 characters

* URI::Parser:: unescape is monkey patched in active support to force the encoding to utf-8 if it isn't by default. Lets set unescape to use ASCII-8BIT

Possible fix for https://github.com/rails/rails/issues/16104
This isn't really testing the problem - it needs to be checking that unescaping a path which contains non-ASCII characters as percent-encoded values doesn't raise a error.