Collapse: Use $.fn.children instead of `>` in selector

Fixes #15131.
split .form-inline .input-group into separate docs example
Filed http://openradar.appspot.com/18987206

Refs #9774
Merge pull request #15137 from twbs/split-inline-form

split .form-inline .input-group into separate docs example
[skip sauce]
upgrade OS X tests to Yosemite

[skip validator]
Merge pull request #15149 from twbs/yosemite

upgrade OS X tests to Yosemite
upgrade iOS tests to 8.1

[skip validator]
Merge pull request #15150 from twbs/ios-8.1

upgrade iOS tests to 8.1
Specify `img` dimensions in the HTML.
Tweak colors to improve accessibility.
Accessibility improvements.