bugfix - don't assign the grandavg helper fields at the beginning, but at the end, since ft_selectdata might remove seom when averaging or selecting a specific parameter


git-svn-id: svn+ssh://svn.fcdonders.nl/home/svnroot/fieldtrip/trunk@9352 0cf7c7f0-3615-4144-b4e6-68da3bce3cd0