fix UnitRange's stop field for release-0.3

[mzaffalon]

backport from 0.4.0 of unitrange_last, fixes #12534
added tests

[tkelman]

Cool, thanks for this. @StefanKarpinski could you take a quick look and say off the top of your head whether this might break or change anything that's currently working on 0.3? It looks okay to me but I wouldn't mind a second opinion.

[nalimilan]

Thanks for the PR. It would be good to mention in the commit message that this copies code from 0.4, and add "fixes #12692" so that the issue is automatically closed after merging.

EDIT: I don't know how I missed that you did that already.

[StefanKarpinski]

@JeffBezanson, this was your change. Does this seem safe to you?

[mzaffalon]

It looks like instead it was reported in #10950, but was not backported (#11261).

[tkelman]

Ah. Well you managed to do it differently than I tried, and according to CI you've avoided the issue I hit.

[mzaffalon]

This also mean that I git bisected wrong and you (@tkelman) were right in finding #10452 weird as the responsible.