I have the same after update to WP 3.6
Confirmed. And I only see this warning if the Rewrite Rules Inspector plugin is installed and activated. Here is a bug report:
Steps to reproduce:
1. Install WordPress 3.6
2. Install the Rewrite Rules Inspector plugin
3. Make sure all plugins are deactivated except Rewrite Rules Inspector
4. Open the dashboard
* Expected: no PHP warnings
* Actual: the following error appears at the top of any page load:
Strict Standards: Declaration of Rewrite_Rules_Inspector_List_Table::single_row() should be compatible with WP_List_Table::single_row($item) in /usr/local/nginx/html/demo/wp-content/plugins/rewrite-rules-inspector/rewrite-rules-inspector.php on line 298
Screenshot:
http://f.cl.ly/items/1W2W19190c1e1B1X130M/Screen%20Shot%202013-08-23%20at%209.51.46%20AM.png
I tried to research this a bit. I found a StackOverflow message that says having the same exact argument default values is important, and if the child’s method hasn’t defined a default value for the first argument then you’ll see a warning like the one above.
http://stackoverflow.com/questions/3115388/declaration-of-methods-should-be-compatible-with-parent-methods-in-php
I compared the single_row function in the plugin and WP 3.6 and I noticed the arguments in the function call are different:
The plugin uses function single_row( $rule, $data )
http://plugins.trac.wordpress.org/browser/rewrite-rules-inspector/tags/1.2/rewrite-rules-inspector.php#L430
While WP 3.6 uses function single_row( $item )
http://core.trac.wordpress.org/browser/tags/3.6/wp-admin/includes/class-wp-list-table.php#L824
Not sure what to do next though. 🙂