Don't show "Manage Locations" tab if the theme has no menu locations defined. props DrewAPicture. fixes #24115.

git-svn-id: http://core.svn.wordpress.org/trunk@24217 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Make the notice on Edit Menus screen more in line with the help text. props DrewAPicture. see #24115.

git-svn-id: http://core.svn.wordpress.org/trunk@24218 1a063a9b-81f0-0310-95a4-ce76da25c4cd