pystencils: fixed problem in pickle/copy support

field.py

@@ -220,7 +220,7 @@ class Field:
             return obj
 
         def __getnewargs__(self):
-            return self.name, self.offsets, self.index
+            return self.field, self.offsets, self.index
 
         __xnew__ = staticmethod(__new_stage2__)
         __xnew_cached_ = staticmethod(cacheit(__new_stage2__))