Base: Placement: change argument order of slerp() in Py

to be consistend with that of C++ one, and of RotationPy

src/Base/PlacementPy.xml

@@ -105,7 +105,7 @@ Placement(Base, Axis, Angle) -- define position and rotation
         <Methode Name="sclerp" Const="true">
 			<Documentation>
 				<UserDocu>
-					sclerp(t, placement2, shorten = True): interpolate between self and placement2.
+                    sclerp(placement2, t, shorten = True): interpolate between self and placement2.
                     Interpolation is a continuous motion along a helical path, made of equal transforms if discretized.
                     t = 0.0 - return self. t = 1.0 - return placement2. t can also be outside of 0..1 range, for extrapolation.
                     If quaternions of rotations of the two placements differ in sign, the interpolation will 

src/Base/PlacementPyImp.cpp

@@ -245,7 +245,7 @@ PyObject* PlacementPy::sclerp(PyObject* args)
     PyObject* pyplm2;
     double t;
     PyObject* shorten = Py_True;
-    if (!PyArg_ParseTuple(args, "dO!|O!", &t, &(PlacementPy::Type), &pyplm2, &(PyBool_Type), &shorten))
+    if (!PyArg_ParseTuple(args, "O!d|O!", &(PlacementPy::Type), &pyplm2, &t, &(PyBool_Type), &shorten))
         return nullptr;
     Base::Placement plm2 = static_cast<Base::PlacementPy*>(pyplm2)->value();
     Base::Placement ret = Base::Placement::sclerp(*getPlacementPtr(), plm2, t, PyObject_IsTrue(shorten));