With recent changes to exception types, unpickling
exceptions that were pickled with an older version
of Python didn't restore all of the original
attributes. Example:

Python 2.4.3 (#69, Mar 29 2006, 17:35:34)
 ...
>>> import pickle
>>> f = open('jar', 'wb')
>>> e = Exception('cucumbers', 'cabbage')
>>> e.args
('cucumbers', 'cabbage')
>>> pickle.dump(e, f)
>>> f.close()
>>> f = open('jar', 'rb')
>>> e = pickle.load(f)
>>> f.close()
>>> e.args
('cucumbers', 'cabbage')

Python 2.5a2 (trunk:46539M, May 30 2006, 05:02:24)
  ...
>>> import pickle
>>> f = open('jar', 'rb')
>>> e = pickle.load(f)
>>> f.close()
>>> e.args
()
>>> e.__dict__['args']
('cucumbers', 'cabbage')

The attached patch fixes this problem, by adding
a __setstate__ method to BaseException. I don't
know if any new tests are needed, since pickling
exceptions is already tested and new tests would
require adding binary files to the test suite.
I did some basic tests that I can attach if
they are needed.

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Removed unnecessary cast.

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Applied as rev. 46585. Thanks!