[web2py] Example broken

[Michal Jursa]

Hi,
just returned back to web2py after some time and browsed examples to 
refresh my web2py skills and found some typo.

1.83.1
images_examples.py uses db.image, which is not present in models:

def index():
    form = SQLFORM(db.image)
    ...

Nothing important, but some new users or beginners can get confused by that.

Michal