Twenty Twelve: fix skewed gallery thumbnail images in IE8 by adding selectors...

Twenty Twelve: fix skewed gallery thumbnail images in IE8 by adding selectors to match attachment thumbnails and any mix-and-match of full-size and large-size image that may occur in content. Fixes #22782.

git-svn-id: https://core.svn.wordpress.org/trunk@23102 1a063a9b-81f0-0310-95a4-ce76da25c4cd