update grid xs mixin and update docs to match new mixins
Merge pull request #9388 from johvik/patch-1

Javascript > Alert should use danger not error
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
Newfangled input and button group sizing (fixes #9295)

Instead of applying `.btn-` or `.input-` to individual elements in
button and input groups, we now have new sizing classes to keep your
markup a little leaner.

* Add `.input-group-sm` or `.input-group-lg` to your `.input-group` to
replicate `.input-sm` and `.input-lg`, respectively.
* Add `.btn-group-xs`, `.btn-group-sm`, or `.btn-group-lg` to your
`.btn-group` to replicate `.btn-xs`, `.btn-sm`, and `. btn-lg`,
respectively.

Both sets of new sizing classes simply use the existing individual
sizing classes as mixins, so customization of them is automatically
inherited when compiling.
Merge branch '3.0.0-wip' of github.com:twbs/bootstrap into 3.0.0-wip
fix spelling
_includes/social-buttons.html: escape ampersands in URLs to fix HTML validation error
Merge pull request #9394 from twbs/valid-github-btn-html

_includes/social-buttons.html: escape ampersands in URLs so HTML validates
social-buttons.html: drop 'px' from height+width attrs per HTML5
fixes #9392: no need for width auto on inline/navbar form controls given inline-block on parent form group
Merge branch '3.0.0-wip' of github.com:twbs/bootstrap into 3.0.0-wip
Merge pull request #9395 from twbs/valid-github-btn-html

social-buttons.html: drop 'px' from height+width attrs per HTML5
undo the grid max-width boundary because it makes offsets kinda borked (you'd have to set twice, for medium and large, in most cases--and that sucks)
Merge branch '3.0.0-wip' of github.com:twbs/bootstrap into 3.0.0-wip
mention #9282 in docs browser section
fix typo; fix caps
safari not webkit
drop the class on the button group toggles CSS (alt fix to #9297)