Reversed HEJ: New generation for jets splitting into exactly two partons

The new algorithm improves the success rate from ~30% to ~75%.
For flat sampling in \Delta R it would be ~50%.

git-svn-id: svn+ssh://svn.hepforge.org/hepforge/svn/hej/MJEV/WJETS/FixedOrderCalc/trunk/ReversedHEJLO@2801 2d6e1942-d43b-4f34-a23d-2688387835af