[Python-3000] Making more effective use of slice objects in Py3k

[Fredrik Lundh]

Guido van Rossum wrote:

> (e.g. you don't seem to appreciate the savings due to a string
> object header and its data being consecutive in memory).

footnote: note that the Unicode string type still doesn't do that (my 
original implementation *did* support string views, and nobody's ever 
gotten around to fully rip it out), so if anyone wants to benchmark 
things related to this specific feature, comparing unicode strings with 
8-bit strings could be someone useful.

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