[issue5218] Check for tp_iter in ceval:ext_do_call before overriding exception message

[Guilherme Polo]

Changes by Guilherme Polo <ggpolo at gmail.com>:


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components: +Interpreter Core
type:  -> behavior
versions: +Python 2.7, Python 3.1

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue5218>
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