[docs] [issue18696] In unittest.TestCase.longMessage doc remove a redundant sentence

[py.user]

New submission from py.user:

http://docs.python.org/3/library/unittest.html#unittest.TestCase.longMessage
"If set to True then any explicit failure message you pass in to the assert methods will be appended to the end of the normal failure message. The normal messages contain useful information about the objects involved, for example the message from assertEqual shows you the repr of the two unequal objects. Setting this attribute to True allows you to have a custom error message in addition to the normal one."

the last sentence duplicates the first one

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assignee: docs at python
components: Documentation
files: issue.diff
keywords: patch
messages: 194748
nosy: docs at python, py.user
priority: normal
severity: normal
status: open
title: In unittest.TestCase.longMessage doc remove a redundant sentence
type: enhancement
versions: Python 3.3, Python 3.4
Added file: http://bugs.python.org/file31208/issue.diff

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue18696>
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