update download_dist for RC 2
update CDN links to point to continuously-updated build; addresses #9138 & its many dupes
don't show download_dist in favor of site.download; addresses #9138 & its many dupes
fix navbar form alignment of inputs by restoring inline-block
fix ID of <select> in fieldset[disabled] example
Merge pull request #9398 from twbs/minor-docs-fix

fix ID of <select> in fieldset[disabled] example
Validation states docs: fix closing tag
add alt text to carousel <img>s
add alt text to thumbnail <img>s
add alt text to media object <img>s
add alt text to <img>s in Images section of CSS docs
Headings docs: use put <hN>s within <td>s instead of <th>s
rm unnecessary blank id attribute
use unique IDs in Forms examples in docs
give navbar forms non-empty `action`s
drop iframe attributes for CSS styling
Merge pull request #9399 from twbs/make-docs-html-more-valid

Make docs HTML more valid
add HTML5 validation of docs pages to the build
add ARIA roles to Dropdown examples in Components docs
add src attribute to holder.js-powered <img>s so that they validate

use `data:` URL of empty invalid PNG: src="data:image/png;base64,"