Scope tablet classes to tablets range only

Fixes #9128
links to Recess repo
link to Uglify-js repo
Link to phantomjs
Merge pull request #9157 from alienlebarge/3.0.0-wip

Add links to Recess, Uglify-js & PhantomJS in README
Merge branch '3.0.0-wip' of github.com:twbs/bootstrap into 3.0.0-wip
Fixes #9150: Hide popover titles in IE8

Properly hides popover titles in IE8 because apparently it doesn't
accept the `:empty` selector. /cc @fat @cvrebert
Fixes #9145: Fix tooltip opacity

Update tooltips to not use RGBa colors so IE8 can have tooltips, too
(means we're now using `opacity`).
fixes #9140: use correct var in tables
Fix #9132, but in the correct branch

People, don't PR against `gh-pages` please!
Merge branch '3.0.0-wip' into 3.0.0-sass-wip

Conflicts:
	dist/css/bootstrap.css
	dist/css/bootstrap.min.css
	scss/_grid.scss
	scss/_tables.scss
	scss/_tooltip.scss
	scss/_variables.scss