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
Not Less' fault per se
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)
add role="tooltip" to popovers; fixes #13481
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