Check patch-8.0.87 for vim 8 job

[janlazo]

Windows releases for Vim seem to always include all patches so it's safe to check only 1 patch to assume the rest are included.

Reference: #666 (comment)

[junegunn]

I don't think the change is needed for non-windows environments.

[janlazo]

What about patch-8.0.45 for non-windows?

[junegunn]

What does patch 45 fix? I'm not sure why we should change the condition. We have confirmed that the Installer using job API works with patch 39 both on non-Windows and on Windows environment (see #534, #541). #594 not working as expected is a separate problem. Anyway, we can conditionally set up s:vim8 depending on the environment if that's required.

let s:vim8 = exists('*job_start') && (s:is_win && has('...') || !s:is_win && has('patch-8.0.87'))

[janlazo]

I choose those patches for #594 which seems to work on the patch-8.0.921 release for Windows.

What does patch 45 fix?

From the patch description in :h patches-8, it fixes job_stop for Vim 8.
Based on the comment for requiring patch-8.0.39 for Vim 8 jobs, I think it's worth considering.

Anyway, we can conditionally set up s:vim8 depending on the environment if that's required.

Simpler to require one more patch for Windows

let s:vim8 = exists('*job_start') && has('patch-8.0.39') && (!s:is_win || has('patch-8.0.87'))

[junegunn]

Thanks for clarification. I tried to separate two issues; Vim 8 installer and s:system using job API (#594).

1. Vim 8 installer works on Vim 8 with patch 39 or above
2. s:system using job API seems to require patch 45 or above

Changing the version requirement from 39 to 45 will make Vim 8 installer suddenly unavailable on a set of Vim versions (patch 39 ~ 44) even they are capable of running it. That was the issue I wanted to address. However, I guess it's not worthwhile to put more if-else statements just for that small range of versions. I'm no longer against changing the requirement.

Having said that, this should be merged with #594 (or equivalent), we don't have to merge it before it.