Don't overlook checkboxes in ordered lists when updating statistics cookie

Don't overlook checkboxes in ordered lists when updating statistics cookie

Manish writes:

> I noticed a small inconsistency.  If you start with following sample
> org file and press C-c C-c in the first cookie, it doesn't get updated
> correctly whereas the second one does.  The only difference is that
> one has children TODO tasks and the other has a list of checkboxes.
>
> Starting file:
>
> --8<---------------cut here---------------start------------->8---
> * Item 1 [/]
>  1. [X] line 1
>  2. [ ] line 2
> * Item 2 [/]
> *** TODO Sub-item 2.1
> *** DONE Sub-item 2.2
> --8<---------------cut here---------------end--------------->8---
>
> Status after C-c C-c in the summary cookie.
>
> --8<---------------cut here---------------start------------->8---
> * Item 1 [0/0]
>  1. [X] line 1
>  2. [ ] line 2
> * Item 2 [1/2]
> *** TODO Sub-item 2.1
> *** DONE Sub-item 2.2
> --8<---------------cut here---------------end--------------->8---