Object identity and misleading default __repr__

I received a bug report via email where the reporter was confused by two links to the same persistent object having different titles (of the form '<package.module.Class object at 0xabcde>' with different memory addresses).

What was more confusing to me was seeing a list of references to different persistent objects all having the same representation:
['<package.module.Class object at 0xsame', '<package.module.Class object at 0xsame', ...]

This happens because the same memory address is reused when we free one Persistent object and load the next one.

Idea: check if the object has a custom __repr__ (via obj.__repr__.im_func is object.__repr__.im_func). If so, use a custom one. For instances of Persistent we could use

    '<%s.%s with oid %x>' % (obj.__class__.__module__, obj.__class__.__name__, u64(obj._p_oid))

I haven't made up my mind if it make sense to hide the memory address of non-persistent objects. On the one hand, all non-persistent objects are different if they're loaded from different pickles. On the other hand, it's possible to have multiple references to the same persistent object within one pickle.