[web] fix muledit rendering bug
form.cw_col might be None and explicitly passing None to the selector
chain may crash. Most __call__ methods of selectors are defined as in :
def __call__(self, cls, req, rset, row=None, col=0, **kwargs)
and then manipulate col as if it's an integer.
Schema of the data
------------------
First take a look at the data schema_ then try to remember that you are browsing
through a heap of data by applying stylesheets to the results of queries. This
site is not a content management system with items placed in folders. It is an
interface to a database which applies a view to retreived data.
.. _schema: schema