Fix flyout menus on most mobile devices.

props ocean90.
fixes #26482.

Built from https://develop.svn.wordpress.org/trunk@27775


git-svn-id: http://core.svn.wordpress.org/trunk@27612 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Proper IDs for the custom fields box.

props SergeyBiryukov.
fixes #14376.

Built from https://develop.svn.wordpress.org/trunk@27776


git-svn-id: http://core.svn.wordpress.org/trunk@27613 1a063a9b-81f0-0310-95a4-ce76da25c4cd