fires closed.bs.alert *after* DOM detach()

fires closed.bs.alert *after* element is removed from DOM.
Previously it fired while the element was still attached.
Fixed navbar radius of example at docs
Remove sr-only from components/dropdowns example

Assuming sr-only is used in the actual live code so that the menu can be
shown open already ... but having sr-only in the highlighted example
code itself is confusing/misleading.

Also, change the text for the button from "Dropdown" to "Dropdown
trigger" for clarity (and it then matches
http://getbootstrap.com/javascript/#dropdowns)
Update alert.js

Added call to remove() after event fires to clean up data as per discussion at #12379
Remove sr-only from components/dropdown entirely

possibly less confusing option, as per discussion, is to always show the
dropdown trigger button (both live and in that code example)
make new Carousel tests compatible with noConflict mode
Merge pull request #13461 from patrickhlauke/docs-dropdown-sr-only

Remove sr-only from components/dropdowns example
bump grunt-css-flip to ~0.2.2
Merge pull request #13433 from watilde/fixed-navbar-radius-of-example-at-docs

Fixed navbar radius of example at docs
Improve accessibility of close buttons in modals & alerts

Adds textual caption to the close buttons. The "X" multiplication sign isn't very meaningful to screenreaders.

Credit: https://github.com/paypal/bootstrap-accessibility-plugin
Per:
    https://github.com/paypal/bootstrap-accessibility-plugin/blob/master/README.md#alert
    https://github.com/paypal/bootstrap-accessibility-plugin/blob/master/README.md#modal-dialog
document #13390
mark Android Firefox as officially supported
Wall of browser bugs: formatting tweaks
Merge pull request #13495 from twbs/android-firefox

Officially support Android Firefox
Merge pull request #13493 from twbs/close-btn-access

Improve accessibility of close buttons in modals & alerts
include RTL CSS CDN URL in Download docs
add RTL CSS files to "What's included" section of docs
emphasize that bootstrap-rtl.css & bootstrap.css should not be used together
Fix .visible-print deprecation version #.
import rules from Ratchet's JSCS config with which we already comply