Listening by default on all the addresses is so bad I don't know why I haven't changed this before. Anyway. Add a `listen on $hostname port $port' syntax to the config file and deprecate the old "port" and "ipv6" global setting. Still try to honour them when no "listen on" directive is used for backward compatibily, but this will go away in the next next version hopefully. At the moment the `listen on' in server context don't filter the host, i.e. one can still reach a host from a address not specified in the corresponding `liste on', this will be added later.

this avoids having the daemon dieing on SIGHUP with a bad config file.

while here also make them a list rather than a fixed-size array.

Was temporarly disabled during the transition to real privsep. While here, fix a memory leak when using `require client ca'. Also, avoid leaking info about the parent address space layout to server processes by not sending pointer values.