[issue28900] update 'docs for other versions'

[Ned Deily]

Ned Deily added the comment:

With the above changes, the sidebar should get updated for the current 2.7, 3.5, 3.6, and 3.7 front pages within the next 24 hours.  I'm leaving this open as a "release blocker" as a reminder to go back and update them all again once 3.6.0 final happens.  I've also added a reminder to PEP 101 to do this.

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stage: needs patch -> commit review

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue28900>
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