Update scrollspy.js

Scrollspy target in tab content does not work properly. Calling .parents('.active') will return all parents with an active class (including the tab pane). Changing this line to .parentsUntil(this.options.target, '.active') should resolve the issue. This will scope the query to only search for active elements inside the scrollspy target.
Added unit test for removing only active class from within the scroll spy key.
Fix: IE10 or lower incorrectly determines the scrollheight of the body. Use document.documentElement for IE. To make this browser agnostic, the maximum scrollheight of both body and documentElement is used.
Fix: IE10 or lower incorrectly determines the scrollheight of the body. Use document.documentElement for IE. To make this browser agnostic, the maximum scrollheight of both body and documentElement is used.
Add Embed responsive utility
Merge branch 'responsive-embed' of https://github.com/boulox/bootstrap into boulox-responsive-embed

Conflicts:
	dist/css/bootstrap.css.map
	dist/css/bootstrap.min.css
Added .list-group-item.disabled

Added support for disabled List group item.
Update variables.less
add .sr-only-focusable; fixes #12259
update docs to include+use .sr-only-focusable
Documents #10140
Merge branch 'master' into document_popover_focus
add posibillity to hover links and not background in list-groups
Defined and use variables for .panel-heading & .panel-footer padding
Fix UAs required message position on grouped radio buttons

Instead of not rendering the element at all with display:none, use opacity:0 and z-index:-1 so the radio element has a defined position on the document and user agents can show the required message in the right place.
replace .visible-{size} with .visible-{size}-{display} ; fixes #8869
switch browserName from "googlechrome" to "chrome" per @Jonahss in #12647
Merge pull request #12834 from twbs/sauce-chrome-name

switch browserName from "googlechrome" to "chrome"
fix #12836

Thanks @Quy.
move grid classes cascade explanation into main grid docs section