[controller] UndoController: fix output method (closes: #1776091) Fix buggy direct output in `UndoController.publish()`. Raise now a ValidationError instead of malformed string Changes: * raise ValidationError when an error occured in undo * use the new message mechanism based on _cwmsgid If errors are not fatal, you have to change publish() method.

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"""cubicweb-%(cubename)s application package

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%(longdesc)s

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"""