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

Fixes #11268: Account for badges within buttons by matching background to text color and text color to background

- Firefox placeholder text is faded out and not the full color. Adding opacity:1 to it returns it to the proper color
- (this is a re-commit since I messed up my branch last time and failed the travis build)

Fixes #10522: Enable use of form validation class on .radio, .checkbox, .radio-inline, and .checkbox-inline

remove comma separating the color and the color-stop in -webkit-linear-gradient in the #gradient .vertical mixin.