I better manage when lists goes out of control and span

We studied the impact of a patch that would prevent a list administrator to add more than LIMIT people to a given mailing list.

This limit would be:
configurable by site administrator thanks to a configuration variable in mailman configuration
only apply to web interface
apply up front: if my limit is 100 and I already have 70 members, when I try to add 31 people at once, none of them are added and I get an error message.
Basically it means that an admin would have no ways to add more than LIMIT people to a list but LIMIT could be crossed if people decide to register themselves by sending a mail to the list.