[issue23704] Make deques a full MutableSequence by adding index(), insert(), and copy()

[Raymond Hettinger]

New submission from Raymond Hettinger:

Attaching an updated patch with documentation updates and tests.

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Added file: http://bugs.python.org/file38617/deque_insert_index_copy4.diff

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue23704>
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