stack: remove unnecessary copying of rdependencies
rdependencies is not modified in any way in this method, so no need to copy it.
This software was downloaded from
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Copyright 2011 Peter Arrenbrecht <peter.arrenbrecht@gmail.com>
Logilab SA <contact@logilab.fr>
Pierre-Yves David <pierre-yves.david@ens-lyon.org>
Patrick Mezard <patrick@mezard.eu>
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