fix whitespace issues

rm some tabs and trailing whitespace prior to a less annoying ;) patch to fix a proxy issue
make it possible to use friend.openid behind reverse proxies

The use of utils/original-url by openid.clj was leading to incorrect return urls.
- document the issue in utils/original-url
- add (:cemerick.friend.openid/return-url req) as an optional override
  to work around the issue.
- fix a potential issue with query string munging in openid/handle-init
- tiny whitespace fixes emacs insists on :)