Scrollspy acting up when targets are hidden

If elements are hidden using `display: none;` which are targets mapped by scrollspy, the plugin might select an incorrect or no menu item.

Checking if the target is visible solved this.
Update affix properly on scrollspy speedy scroll to top of page #11310

Fix scrollspy.js so as affix is updated properly when user scrolls fast
to top of page.

A fix for issue #11310.
Allow listbox AIRA role on dropdown component.
grunt on last merge
fixed .clearfix example, + doc link
Merge two fs variable declarations into one

One is enough.
Merge pull request #12035 from tomByrer/master

fixed .clearfix example, + doc link
drop the title
fixes #10658 jQuery Popover content loses bound events on second setContent call.
Merge pull request #11203 from jasny/patch-1

Scrollspy acting up when targets are hidden
Merge branch 'master' of https://github.com/twbs/bootstrap
Rearrange repository contents because muahahahahahaha
Streamline copy process by not bringing over full files into docs/dist/, only take minified ones
no more page.base_url
fixes #11288 - Vertical scroll position of modal saves between openings
Merge branch 'master' of github.com:twbs/bootstrap
Merge branch 'scrollspy-speedy-scroll-top' of git://github.com/ziogaschr/bootstrap into ziogaschr-scrollspy-speedy-scroll-top

Conflicts:
	dist/js/bootstrap.min.js
fixes #11373 - adds related target to dropdown events
fixes #11379 - Fix carousel this.sliding not getting reset if $next.hasClass('active')
Merge branch 'dropdown-aria-roles' of git://github.com/plumlee/bootstrap into plumlee-dropdown-aria-roles

Conflicts:
	js/dropdown.js