Code review of Domain Relationships

Attached is a patch that is the result of both a strict code review in Coder, a code review with code-style.pl and a bit of manual code style review.

I feel that this code is more in line with good coding practices, more readable etc - but any feedback is much appreciated!

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This patch is the result of around two days of work to upgrade and improve the Domain Relationships module to get some new features which we at Good Old needed for a customers site. This is one of many patches for improvements that I'm separating out of my staging git-repo: http://github.com/voxpelli/drupal-domain-relationships