Add equals function to group and subgroup

Don't clear and addAll at each subgroup addition of groupList
Performed removed non informative sub-group after finish grouping.
Now, all work fine and are reproductibly.

git-svn-id: https://subversion.renater.fr/xtandempipeline/trunk@301 b8ef2a07-7df7-436f-90b9-41648038564b