Undefined name: pages --> slideshow.pages
Undefined name: pages --> slideshow.pages

$ `flake8 . --select=E9,F63,F7,F82 --show-source --statistics`
```
./www/slideshow/en/slideshow.py:80:24: F821 undefined name 'pages'
        page_num = len(pages)-1
                       ^
```
@schmave Your review, please.
brython-dev/brython,brython-dev/brython,brython-dev/brython