Use jQuery.on() properly in accordion code. Some other cleanup.

see #23890.

git-svn-id: http://core.svn.wordpress.org/trunk@23856 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Compress scripts/styles: 3.6-alpha-23857.

git-svn-id: http://core.svn.wordpress.org/trunk@23857 1a063a9b-81f0-0310-95a4-ce76da25c4cd