upstream bash-completion patches

[andychu]

I was reminded me of this since neofetch accepted some patches ( #679 ), and as of Oil 0.8.pre4, we have $OIL_VERSION.

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I have a year-old fork here:

https://github.com/oilshell/bash-completion/

But I believe it shouldn't be that out of date, because the changes are mostly in one file (and also because bash-completion is a decades-old and stable project). As far as I remember, I implemented the compadjust builtin in Oil to do what a few hundred lines of bash did there.

TODO: look at the code again :)

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I still want completion with descriptions like zsh and fish, which bash doesn't allow for. #315

But I think people will use bash-completion for a long time, so this is worth doing.

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carrot for upstream: coverage #687 . They have automated tests, so seeing coverage info would be useful.