Incorrect margin-left and margin-right on .row-class when using odd @grid-gutter-width

[malthejorgensen]

Steps to reproduce

1. Choose an odd @grid-gutter-width, e.g. @grid-gutter-width: 15px
2. Compile bootstrap Less-stylesheets

Problem
The left and right margin .row class, which should normally "cancel out" the left and right padding of the .col-*-* classes is actually flipped so that instead cancelling out, there's a one pixel difference between the two:

.row {
  margin-left:  -7px; /* should be -8px */
  margin-right: -8px; /* should be -7px */
}

.col-md-12 {
  padding-left:  8px;
  padding-right: 7px;
}

Reason
The reason why this happens is that in .row the ceil() and floor()-functions are used on negative numbers: margin-left: ceil(-7.5px) == -7px, as opposed to the .col-*-*-classes where it's used in a standard way on positive numbers: padding-left: ceil(7.5px) == 8px, which ends up giving the one pixel difference. As ceil()/floor() rounds towards negative/positive infinity, rather than towards/away from zero.

The bug was introduced with the fix for: #16281

[mdo]

Bootstrap 3 is essentially in maintenance mode as we focus on working towards a stable v4. As such, we're only accepting changes to v3's code on a case-by-case basis, usually only for critical bug fixes or docs improvements.

Sorry for the inconvenience, and thanks for the suggestion, but we'll be passing on this change.

<3