[issue25671] Fix venv activate.fish to maintain $status

[Stéphane Wirtel]

Stéphane Wirtel added the comment:

I am a user of fish.

The use case is just execute python -mvenv demo 
source demo/bin/activate.fish

check the status and deactivate the virtualenv ?

do you confirm ?

Thank you

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nosy: +matrixise

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue25671>
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