and fix the operator< implementations in some of the other
plugins too.

Change-Id: Ie5631e0cdc8d2a994ad2af2533cdb558a6cfc035
Reviewed-on: https://gerrit.libreoffice.org/25057Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>