Temp drag. Some tests fail (test_advection_nullVelocity,...

Temp drag. Some tests fail (test_advection_nullVelocity, test_advection_randomVelocity) following merge with JM branch. To be fixed

HySoP/hysop/operator/drag_and_lift.py

@@ -18,7 +18,7 @@ class DragAndLift(Computational):
     The present class implements formula (52) of Plouhmans2002.
     Integral inside the obstacle is not taken into account.
     """
-    def __init__(self, velocity, subsets, formula=DragAndLift.Momentum,
+    def __init__(self, velocity, subsets, formula=None,
                  vorticity=None, **kwds):
         """
         @param velocity field