An equivalent to tubeamp's commandline fix works if I use the correct name for my touch pad, namely,
xinput set-button-map "AlpsPS/2 ALPS DualPoint TouchPad" 3 2 1 4 5 6 7 8 9 10 11 12
(I got the name by running
xinput list | grep 'id=' )
Of course this is not a solution, only a very unsatisfactory workaround ...
which leads to the question:
As long as this bug is considered "low priority",
where can either the xinput command, or an .fdi file that fixes the problem, be put so that the mouse buttons are swapped at login, and the swap is not sabotaged by a dysfunctional gnome-control-center?