Prevent horizontal scrolling when the responsive sidebar is open, pushing the main column off to the right. See #25858.

git-svn-id: https://develop.svn.wordpress.org/trunk@26423 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/css/wp-admin.css

@@ -12227,6 +12227,12 @@ li#wp-admin-bar-menu-toggle {
 		display: block;
 	}
 	
+	/* Disable horizontal scroll when responsive menu is open
+	   since we push the main content off to the right. */
+	#wpwrap.wp-responsive-open {
+		overflow-x: hidden;
+	}
+	
 	html.wp-toolbar {
 		padding-top: 0;
 	}