[repo, undo] Finish repository-side implementation of the undo feature (closes #893940) 1) Changes API for undo_transaction in order to raise an exception: the previous API returned a sequence of error, the user of the API needed to be careful to check explicitly. We change this for it to raise an UndoException with the list of errors as an attribute. 2) The server-side support for undoing update actions is finished 3) The configuration for `undo-support` is now a simple boolean Beware of the costs, both in DB space and in number of requests on the RDBMS backend, once this feture is activated. 4) Adds a txuuid param/attribute to the existing NoSuchTransaction exception.

/var/log/cubicweb/*.log {
        weekly
        missingok
        rotate 10
        compress
        delaycompress
        notifempty
        create 640 root adm
        sharedscripts
        postrotate
           if [ -x /usr/sbin/invoke-rc.d ]; then \
              invoke-rc.d cubicweb reload > /dev/null 2>&1; \
           else \
              /etc/init.d/cubicweb reload > /dev/null 2>&1; \
           fi; \
        endscript
}