Fix issue with tagbar changing the global scrolloff value.

[raven42]

Closes #693

Tagbar is overwriting the global scrolloff value which can affect other windows. Change the behavior so it does a setlocal instead when needed so this only impacts the tagbar window

[Shane-XB-Qian]

looks this change did not work well, e.g set scrolloff=0 at line#2126
did not dig code detail, just chk looks it seems like that .. and influenced others windows if set value to this option.

[raven42]

@Shane-XB-Qian can you please elaborate? This change was to update tagbar to use setlocal instead of set so it is not changing a global setting.

[Shane-XB-Qian]

sorry, i have no time to dig detail, but for now obviously not correct:
you can e.g start vim with let g:tagbar_scrolloff=16 and set so=10, you can see globally value had been influenced.

[raven42]

@Shane-XB-Qian I think you must have not pulled in this fix. This fix specifically fixes the issue you are referring to. The g:tagbar_scrolloff field was introduced in #692. But this fix was to correct the behavior which already existed in the tagbar code where it was setting the global scrolloff. Please make sure you pull in the latest and try again. I tested with the values you specified and when I issue a echo &scrolloff in the tagbar window, I see 16, and then without changing anything if I issue that in another window, I see a value of 10.

[Shane-XB-Qian]

// I got upt 13hours ago, your latest pr was 23hours ago.
What this let &l:scrolloff = scrolloff_save for?
And check line#2126 there is set scrolloff=0 too.
I felt a little mess now, and not sure why you can get 10.
I felt those code original author was trying to save &so value, then zt, then recover.
Anyway, I am not near my computer now, wish you can review/check again.

[alerque]

What this let &l:scrolloff = scrolloff_save for?

That sets the buffer local scroll off value to the previously saved value.

And check line#2126 there is set scrolloff=0 too.

This is a second instance of the problem we were fixing. This PR fixed one instance, that is a different one.

I felt those code original author was trying to save &so value, then zt, then recover.

The original code was saving a value, setting it to something else, doing the action, then restoring the value. The problem was the set it was doing was a global set instead of a local one, then restored it also by doing a global set instead of local.

@raven42 The instance you fixed is in s:RenderContent(), the one tripping up @Shane-XB-Qian is another instance of the same kind of error in s:RenderKeepView() that we didn't touch at all.

[raven42]

Honestly I'm not sure the purpose of this little block of code. I found this while looking at another issue and thought I'd fix it so we aren't changing the global scrolloff value.

[raven42]

I've pushed up another PR (#697) that will address the other instance of this bug. I've also looked for any other instances where the scrolloff is being adjusted, and this looks like the only other place.