golem95: Add different find_grand_plus methods (computation_variant).

This introduces "computation_variant" (module parametre)
which chooses between different method of find_grand_plus
(module matrice_s) for estimating numerical stability.

git-svn-id: svn+ssh://svn.hepforge.org/hepforge/svn/gosam/gosam-contrib-2.0@900 a6e02f90-e1d0-4296-904b-e314d7e4afaa