Fix usage of "absolute URL" in the documentation

[Malcolm Tredinnick]

Django's documentation is using the term "absolute URL" in a way that is inconsistent with existing standards. We should fix that; it leads to errors too easily.

The relevant definition to apply is in section 3 (and also section 1.4) of RFC 2396: An absolute URI includes everything from the scheme ("http:", etc) onwards. All other URIs are relative.

Documentation that needs to be updated

• get_absolute_url() -- all our examples are relative and absolute URLs are in the sites documentation. Add a link between the two and some explanation.
• The location field in sitemaps.
• A few places in syndication_feeds.txt

This are all purely documentation/explanation changes. We aren't doing anything fundamentally wrong in the code (outside of HttpRedirect) that I know of.

[David A Krauth]

It appears that Malcom has already added this documentation for the unicode merge.