[Twisted-web] memory leak with metaclass

[Paolino]

tazzo wrote:
> Also without metaclass there is a memory leak, returning
> instances of rend.Page from locateChild they are never released.
> Here a simple example, the function 'do' build on file log
> a simple statistic every 5 sec about only instances classes  that are
> growing up during page serving.
> Try to start the server and ask some page continuosly, you'll see
> the number of rendPage grow up with some other classes.

Thanks to the interest of dialtone and exarkun the leak has been removed 
for both tests in revision  1582

This means  creating (and destroying) Page derived classes and their 
instances doesn't lead to a server growing on every request.

Pytypus gang thanks them.