These vsprite structure members are reserved for system use (do not write
to them):

    nextvsprite and prevvsprite -- these are used as links in the
                                   gelsinfo list.

         drawpath and clearpath -- these are used for bobs, not true
                                   VSprites.

                  oldy and oldx -- previous position holder, the system
                                   uses these for double buffered Bobs,
                                   but application programs can read
                                   them too.

The values can be set like this:

    myVSprite.NextVSprite = NULL;
    myVSprite.PrevVSprite = NULL;
    myVSprite.DrawPath  = NULL;
    myVSprite.ClearPath = NULL;
    myVSprite.OldY = 0;
    myVSprite.OldX = 0;