These two classes inherits from two classes implementing CopyContainer API:
- ours, via low-priority bases
- another one, via higher-priority bases, because these classes need
  some non-ERP5 methods to override ERP5 methods.
So after defining these classes, resolve inheritance priority by binding
all CopyContainer methods provided by their ERP5 base class, overriding
the ones provided by their non-ERP5 bases while still allowing their ERP5
base class to override the CopyContainer method.