[issue29853] Improve exception messages for remove and index methods

[Serhiy Storchaka]

Changes by Serhiy Storchaka <storchaka+cpython at gmail.com>:


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resolution:  -> duplicate
stage:  -> resolved
status: open -> closed
superseder:  -> Non-informative error message in index() and remove() functions

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue29853>
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