Fix issue #883, add/sub seconds/minutes/hours should handle DST correctly

[knutdx]

I know there already is a pull request on this (Ovsyanka@eb6581b) but I think my solution may be cleaner. Seems to me that DateTime::modify is really bad when it comes to DST, so it is better to do these addXxx and subXxxx operations with timestamps instead. Since timestamps doesn't have timezone and doesn't care about DST.

[KnutHelland]

The failing tests now are not because of code, but because of misconfiguration of the CI

[Glavic]

@knutdx: can you please rebase? TY

[Ovsyanka]

I don't think it is good approach because it will be inconsistent with the DateTime default behaviour. And you just came to decision we already tagged as wrong. Look at #883 (comment) There is lot of discussions, I suggest you to read it carefully.

[KnutHelland]

Fyi: when I submitted this pull request, I altso added a bug report and a merge request to phps timelib to fix this issue: https://bugs.php.net/bug.php?id=75167 there is a really ugly (and easy to fix) bug in timelib here, and it is annoying that noone has fixed it. Almost feels like the datetime library in php is abondoned.

[KnutHelland]

Pull request to the timelib used in php source: derickr/timelib#24

[KnutHelland]

So at least I think carbon could do a hack to compensate for that bug

[KnutHelland]

Sorry for all the comments, but I also have to say that I don't longer work with PHP and don't have a environment to test these things any more (and don't have access to that old work-account on github neiter), so I'll not rebase. But seems like you don't need it after all...

[kylekatarnls]

modify finally removed, we will kept the PHP native behavior and adopted it in the diffInSeconds/Minutes/Hours method all using intervals now.

So this could be done in other methods? For now, I have no better ideas than the following names:

addRealSeconds
addRealMinutes
addRealHours
diffInRealSeconds
diffInRealMinutes
diffInRealHours

So I will open a new issue for this and close this one.