Use sh_binary to wrap run scripts for windows support.

[christopherschwaab]

Windows is silly and falls over scripts that aren't wrapped in an exe runner. Wrapping multirun/command with sh_binary should make them usable on windows (at least with msys2 here on 5.1.0) and I think should be benign on saner platforms. Thanks!

[ash2k]

I think the tests are failing because shell(s) do not propagate some signals. I don't know if there is a way around it.

[christopherschwaab]

Oops, excuse me I'd meant to get back to this but got caught up in other work. I very well may be overlooking something else but it appears that perhaps also the file extension is now wrong in those tests (since on windows it's wrapped in a launcher which has an .exe at the end). I'll have a look at updating the tests when I have a chance hopefully over the weekend.