I found some operating systems does not allow to accept IPv4 client on IPv6 sockets or some system are configured in such manner (like GNU/Debian). Also I think it can be helpful to bind Privoxy to certain addresses only or to more ports.
There is similar item #71 on TODO list. My implementation forces to bind to all listed addresses. However it could be possible to adjust it.
I performed only few tests so there can be some bugs.
I will attach series of 5 patches against latest CVS tree.