Socket: more fixes for win32/aos3 These special snowflakes have specialised socket close APIs, so ensure that we use the correct one. Additionally, there's no guarantee that their socket() API signature matches the POSIX definition, so wrap it up and cast the result.
RISC OS: use SocketWatch for socket activity Use SocketWatch to monitor our sockets and convert activity into a pollword update. This allows us to ditch the schedule-based fetch path and take the same one as we do on other platforms. This also allows us to refactor the main poll loop such that we need only poll idle while waiting for things to happen (once something has happened, we poll aggressively until there are no non-pollword events left).