[issue4978] allow unicode keyword args

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc <amauryfa at gmail.com> added the comment:

Sorry, but _PyUnicode_AsDefaultEncodedString returns either a borrowed reference (if 
errors==NULL) or a new reference (if errors!=NULL).
In either case it's wrong to DECREF the string when you simply take the buffer's 
address:

>>> f(**{u'someLongString':2})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() got an unexpected keyword argument 'ÛÛÛÛÛÛÛgString'

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue4978>
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