Sanitize rails env variables

Hi,

The following PR adds ORIGINAL_FULLPATH and ORIGINAL_SCRIPT_NAME to the list of URI_FIELDS to sanitize.

Note that these are added by rails here https://github.com/rails/rails/blob/99dccf1aae31520b701fc37e62542db1e6c0994f/railties/lib/rails/application.rb#L162

We were having "incompatible character encodings: UTF-8 and ASCII-8BIT" errors caused by using "request.original_url" and IE sending non-ascii characters.

Thanks for your work.