This is an example module for file system based storage for 
messages. It uses the file atime vs. mtime to determine whether a 
messagee is new.

This module lacks delete-locking of an open message 
directory, which means that its possible to delete a message in
one call and on a parallel call not be able to listen to that 
deleted message any more (even if it was in the list before). This 
should be very rare usage though.