change to VecScatterBegin/End

The prototypes for VecScatterBegin() and VecScatterEnd() are now changed. This change is made to have these routines consistant with PETSc calling convention [i.e the first argument should be the appropriate object for that functionality]. i.e: PetscErrorCode VecScatterBegin(Vec,Vec,InsertMode,ScatterMode,VecScatter); to PetscErrorCode VecScatterBegin(VecScatter,Vec,Vec,InsertMode,ScatterMode); Satish