Fix of HELIO parse

#1158 but to master
I'm not really sure.  [What I've found](http://stackoverflow.com/questions/1793261/how-to-join-components-of-a-path-when-you-are-constructing-a-url-in-python) is `urlparse`, but if the `service.lower()` for some reason starts by a `/` then it will remove everything in `RL.LINK` till the root. Which is not what we want.  It seems to me that the simplest and clearer option is this way.