Fix unquoting arguments before passing to shell

[nuid64]

#7453
Now quotes all arguments passed to the shell

[the-mikedavis]

This changes the behavior and limits the usefulness of :sh: :sh echo "$EDITOR foo" for example will no longer expand $EDITOR because of the single quotes.

I believe the way to fix this is to have a way to disable shellwords for the :sh command. We shouldn't try to process any of the text passed to :sh.

[pascalkuthe]

I think we still want some very basic processing so that #6979 can be used with :sh. i think kakune simply splits whitespace and only replaces (%...) when needed

[nuid64]

Do we want " act same as '?

[pascalkuthe]

Mike was just giving an example. There are lots of similar edge cases. I was about to make a similar comment. Simply forwarding the arguments to the shell unchanged (with the minor exception I mentioned above) is the only consistent and intuitive solution IMO

[nuid64]

We could just not trim the quotes when parsing shellwords. Is it a good solution?

[the-mikedavis]

No, the quotes should be dropped where shellwords are actually used. For example :open "a b.txt" should open a file a b.txt but with that change it would open "a b.txt" (where the quotes would be part of the filename).