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

 - i_resp_previously, previously should include which tags ?
     replay prevention  all of them
 - rpush negotiation for which tag to sign
 - test suite tests/lib
 - many actual tests

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

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