Document broken "outdent" with multiple navbar-right classes

Created by: fleaflicker

First reported in #12947 . Resubmitting with an example and more details as requested by @mdo .

http://jsfiddle.net/D2RLR/5339/ (this is a pure CSS issue, but you'll need to expand your viewport so that the navbar is not collapsed)

The example shows the navbar from the docs but with one change -- the form is pulled right with .navbar-right.

I believe the intent of all the negative margins on .navbar-right is so that the right-most one will go up to the right edge of the navbar.

It works with just one .navbar-right element, but not with two or more because right floated elements appear in reverse order from their markup order.

In the example, the `.nav' items are shifted right 15px. They should not be but the form should be shifted right 15px.

Relevant excerpt from navbar.less

// Outdent the form if last child to line up with content down the page
&.navbar-right:last-child {
      margin-right: -@navbar-padding-horizontal;
    }

The negative margin should apply to the first element with the .navbar-right class. But I'm not sure how to select that.