Dropdown menu in justified button-group

It seems that dropdown-menu in justified button-group appears at the far
left of the group. Check the problem in [Bootstrap
site](http://getbootstrap.com/components/#btn-groups-justified).
Fixed affix-bottom positioning

Set top position to (scrollHeight - this.$element.height() - offsetBottom).
Squashed commit of the following:

commit 81324491f4913d6797c3c9e4df83a1aefd7d9116
Author: Daniel <dano.husar@gmail.com>
Date:   Sat May 10 17:37:29 2014 +0100

    use opacity mixin

commit 694b0a3fcd196e8cba9e4c23850f903c0804cb44
Author: Daniel Husar <dano.husar@gmail.com>
Date:   Fri May 9 13:47:35 2014 +0100

    Update button-groups.less
Merge pull request #13541 from gpakosz/patch-2

Fixed affix-bottom positioning
Merge pull request #13549 from danielhusar/master

IE8 button group support
cleanup
Temporarily revert README deletions from #13470,
pending the release of v3.2.0's updated hosted docs.

Fixes #13572.
fixes #12211: Scrollspy: Navs in different tabs can interfere with each othe
Merge pull request #13576 from twbs/fat-12211

fixes #12211: Scrollspy: Navs in different tabs can interfere with each ...
nuke rtl
Merge branch 'master' of github.com:twbs/bootstrap
grunt
nuke the rtl docs
nuke the rtl example
remove the comment
Merge pull request #13369 from armikbd/bootstrap-itsme

Dropdown menu in justified button-group
grunt dist
Enable clean-css's advanced optimizations.