Tag rename unfinished business
(things resulting from searching for `tag' where searching for
 `debiantag' wouldn't find them)

 - protocol version 4
      implies ability to sign new tag (this is already there
         so simply advertising version 4 will work)
      needs also new ability to sign old-format tag in split
         brain way

 - test suite tests/lib
 - many actual tests

 - other tag should be [dgit Maintainer-Tag quilt=$quilt-mode]


Want tests for
 - accepting old and new version tags
 - rejecting push of same version with one tag when then the other

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Provide --gpbpq[=:] options
Document --quilt=unapplied|gbp|dpm