[HttpFoundation] Request - URI - comment improvements

Hi all,

I was wondering why there is a difference between the URI's given by the `Request` object.

The method `getUri` will give a URL so  including scheme,http host and base URL, for example:
`http://dev.decorrespondent.nl/verleng?a=1`

While the method `getRequestUri` will give:
`/verleng?a=1`

While both correct it can get confusing, that is why I propose these copy changes in the comments.
urn is something different