Immediately close a flyout when opening another one. Prevents brief occurrence of two flyouts at once. Props SergeyBiryukov. fixes #19575 for trunk

git-svn-id: https://develop.svn.wordpress.org/trunk@19647 602fd350-edb4-49c9-b593-d223f7449a82

wp-admin/js/common.dev.js

@@ -209,6 +209,7 @@ $(document).ready( function() {
 			else if ( m.css('marginTop') )
 				m.css({'marginTop':''});
 
+			menu.find('.wp-submenu').removeClass('sub-open');
 			m.addClass('sub-open');
 		},
 		out: function(){