Updated compatible versioning strategies document

It's at
http://www.w3.org/2001/tag/doc/versioning-compatibility-strategies-20080513.html

and the latest is at
http://www.w3.org/2001/tag/doc/versioning-compatibility-strategies

I incorporated the large majority of comments from Marc de Graauw, Ashok,
Noah.  I was not able to incorporate any comments from Norm as I think he
and I need to discuss his comments further.  The material is modestly
revised so I think another review by Norm is still useful.

This completes my action to revise the material by EOD tuesday so that Dan,
Raman, Noah and Norm can do their reviews in time for the f2f.

Cheers,
Dave