[issue4016] improve linecache: reuse tokenize.detect_encoding() and io.open()

[Antoine Pitrou]

Changes by Antoine Pitrou <pitrou at free.fr>:


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priority:  -> normal
stage:  -> patch review
versions: +Python 3.1 -Python 3.0

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue4016>
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