This is not EOF, and never should have been so -- can trip up other code
when porting.
Also updates LibGUI and WindowServer which both relied on the old
behaviour (and didn't work without changes). There may be others, but I
didn't run into them with a quick inspection.
Make the Socket functions take a FileDescriptor& rather than a socket role
throughout the code. Also change threads to block on a FileDescriptor,
rather than either an fd index or a Socket.
If connect() is called on a non-blocking socket, it will "fail" immediately
with -EINPROGRESS. After that, you select() on the socket and wait for it to
become writable.
