Closes #18887

Add Wall of Browser Bugs entry for #18543

https://connect.microsoft.com/IE/feedback/details/2256049/edge-ie11-viewport-rule-has-side-effect-of-making-scrollbars-auto-hide
[ci skip]

Fix active Home tab in narrow-jumbotron example

This reverts commit e7b0d726.
Closes #17022
[ci skip]

Rename gradient mixins to match new naming convention

Respect $border-rounded inside progress bars too

rm unnecessary border-radius properties from .btn-group-vertical code

v4: Custom forms variables

Update docs to include mention of the custom variables file

Merge branch 'provide-custom-scss' of https://github.com/stephaniepurvis/bootstrap into stephaniepurvis-provide-custom-scss

Prevent breadcrumb separator from getting underlined on hover when not using <ol> markup

Use proper variable for .dropdown-backdrop's z-index

Remove near-duplicate contextual list group example

Add variables for miscellaneous box-shadows

[skip sauce]
[skip validator]

Add variables for padding of popover title & content

Add variables for media object margins and padding

the active class should be moved from the list item to the link item

Docs: Use mixin syntax in Sass example of .invisible

[ci skip]

$enable-gradients docs: Add missing word

Fix RVM under Travis caching by excluding node-which from $PATH

See https://github.com/travis-ci/travis-ci/issues/5092 for more details.
Reverts #18376

Docs typo: from controls --> form controls