[docs] [issue27528] Document that filterwarnings(message=...) matches the start of a message

[Martin Panter]

Changes by Martin Panter <vadmium+py at gmail.com>:


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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue27528>
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