With this patch, stream and listening sockets handle the setup of
accepted sockets internally. Sub-classes of |StreamSocket| don't
have to overload StreamSocket's |GetIO| any longer.
This patch integrates |ConnectionOrientedSocket| into the hierarchy
of socket I/O classes. In future patches, the class can provide
common interfaces and functionality for all connection-oriented
sockets.
The new class |ListenSocket| listens on Unix sockets for incoming
connections. Accepted connections are handed over to a compatible
connection-oriented socket.
