take liuqe from expression if not explicitely specified, liuqe.m2 is used if in expression to set liuqe 2, enforces liuqe if given in parameters

git-svn-id: https://spcsvn.epfl.ch/repos/TCV/gdat/trunk@8142 d63d8f72-b253-0410-a779-e742ad2e26cf