Stage 3 Proposal 21: Resolve inconsistent class values for shortdesc, linktext, and searchtitle

I have prepared the stage 3 draft of this proposal and committed it to SVN.
I need volunteers to review this draft.
This is a very simple change to grammars--there is no specification change, so a very easy proposal to review.
The RNG grammar changes are current on this pull request: https://github.com/oasis-tcs/dita/pull/309 Cheers, E.

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Eliot Kimber http://contrext.com