FIXES #12992

added .transition-timing-function(@timing-function) mixin, defaults to @timing-function.

The col-*-push-0 and col-*-pull-0 classes try to reset the positioning using 0% but this prevents the opposite direction positioning to freeze and not being set correctly.
To fix that, these must set the position to auto instead of 0% with means left:auto and right:auto instead of left:0% and right:0%.

I think that's the only animation property that was missing and it's quite useful.

https://developer.mozilla.org/en-US/docs/Web/CSS/animation-fill-mode

No need for old Firefox versions support.

New stuff:

* Adds `.has-feedback` and `.form-control-feedback` to show icon-based
form feedback to users. Fixes #11836.
* Removes the `width: 1em` on `.glyphicon` because it makes it
impractical to resize the width of all icons, even if they’re not
“empty” (e.g., a simple `.glyphicon { width: 30px; }` wouldn’t work,
nor would a class preceeded by a parent class.

Clean up:

* Sets `width: auto;` on all `.form-control`s within inline forms.
* Removes all the inline `select` menu `width` styles because all
inputs are now `auto`.
* Update form states docs to separate out sections better.

<3 @seven-phases-max for helping to confirm & debug this
X-Ref: https://github.com/less/less.js/issues/1725

Original discussion:
https://github.com/less/less.js/issues/1437#issuecomment-21383639.

Since we’re switching to `grunt-contrib-less`, we can take advantage of
newer LESS features than what RECESS supported. Included in that is the
ability to `:extend`, and not only that, but `:extend(.mixin-name
all)`. By doing so, we remove duplicate CSS for all our elements that
were being clearfix-ed.

Fixes #8947, #8968, #8991, #9257, #9268, #9291, #9430, #9604, #9686,
#9929, #10731, #10793, #11305, #11498, #11533, #11570, #11604, #11652.

(dem issues, tho)

* Adds nav link to sidebar for contextual classes
* Refactors to use prefixed classes, like .list-group-item-info, instead of chained classes
* Adds default and linked variations to example in docs

Fixes #11766: Use color var for background on badges in buttons to restore proper background to default button badge

reverted changes in commit 96109d31 which seemed to break conditional classes in striped tables (ignoring the comment above that the previous rules were needed for just this purpose)

fixes issue #11728

http://caniuse.com/#search=grad