Suggested changes to Relationship help documentation [#1293654]

Here are some proposed edits to the relationship Help content. I move a couple of things around, mostly in the first four paragraphs. Most of these changes are in the newly created Included Relationships section -- the current version was confusing (to me). I did not include any changes to the examples.

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Relationships expand a query to include objects other than the base query.

Included Relationships

Unfortunately, the concept of relationships is made more difficult because Views includes some by default. For historical reasons, it would be inconvenient to remove these default relationships.

The best example of a default relationship is the node-->user relationship. When a node is in the query, the author who created it is automatically made available. [Note: it was an error that this relationship is automatic, but by the time the error was found, it was too late to change it.]

A relationship that is similar but not automatically made available is related to node revisions. Each revision has its own author, i.e. the user who made the revision. By adding the "Node revision: User" relationship, all of the 'user' fields, sorts, filters and arguments will now be available for the revision author.

Use

When a relationship is added to the view, all applicable items gain a "Relationship" select box to choose which version of that particular item to use. Each item defaults to using no relationship.