new draft of Interoperability section

All,

I'm attaching a new draft of the Interoperability section. Miguel has  
developed this one on top of Oscar's FPWD text and taking into account  
open issues around the topic.

I intend to integrate this one and the Multi-Channel one into the  
Editor's draft asap, so all could refer to the text there for  
subsequent comments.

Please, note that this one affects a number of open ISSUES: ISSUE-1,  
ISSUE-7, ISSUE-8, ISSUE-9, ISSUE-21. I'll review how changes relate to  
them one by one in separate messages.

-- Jose

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