windows: make it possible to send pipe handles over ipc pipes

[piscisaureus]

Needs a refactor of the ipc protocol.

[BobDickinson]

I'm starting to develop the opinion that this is the root of the issue that I reported against iisnode. I based a pretty large part of the design of my current project on the concept that I would be able to pass a handle (a socket) over the IPC to a child process, as is well covered in the node docs. This all worked fine until I tried to deploy it to Azure, which virtualizes the socket plumbing such that your node app listens on a pipe (instead of a TCP port). The sockets that you get on connections to that pipe look and work exactly like TCP sockets, except that they apparently cannot be passed to a child process via child.send(message, handle). This was especially frustrating as the handle I was passing was a net.Socket and took the same internal code path through send(). I didn't even know that it wasn't a TCP socket under Azure until I'd done quite a bit of debugging.

As someone who invested quite a bit of time, both in designing a system based on this approach and on tracking down why it isn't supported, I would have very much appreciated seeing this limitation called out in the docs. Maybe: "On Windows named pipes are used for IPC (via libuv), and that implementation has a number of limitations, including limitations on the kinds of handles that can be passed via send()".