Add a class based on $i in menu render

As I could'nt find any way to override menu render into menu_block's blocks() I made a one-line patch to add a class child-$i to menu elements.

I really needed this class, and this part of code is not themable, so I had to do this. This has sens, as the module already add 'first' and 'last' classes.

Is there any way to do it with a proper theme() function? If no, is it possible to apply this patch to future releases?

Attached, the patch, based on 6.x-2.2 version.