Twenty Thirteen: move IE-specific properties out of main stylesheet. Props obenland, see #23507.

git-svn-id: http://core.svn.wordpress.org/trunk@23611 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Thirteen: adjust caption color in footer widgets, props obenland. Fixes #23660.

git-svn-id: http://core.svn.wordpress.org/trunk@23612 1a063a9b-81f0-0310-95a4-ce76da25c4cd