Since you would need to re-register when changing the app name, we will
switch the setting name to growl_net_name so that all growl_net_*
settings require /growl-register which makes explanation easier.
Since we're now using IO::Socket::PortState, we can more easily
register to the default values without worrying that irssi will block
until it fails. Having growl automatically send a registration message
when it loads seems more natural.