Use poll(2) for timeouts on socket

[alanxz]

Use poll(2) instead of select(2) to do timeout operations on sockets. This helps
with the situation where the fd is larger than FD_MAXSIZE.

Fixes #168

[abogosyan]

Will it work on Windows?

[alanxz]

Not yet... (which is why this isn't in the master branch yet).

winsock2 has a poll implementation, however its only available in Vista/Server 2008 and later. I need to consider whether to support Win32 clients older than Vista, and consider providing an alternate implementation for those systems that don't support it.

[mclassen]

For Windows, you can actually just define FD_SETSIZE to a larger value, which works. On Linux it doesn't work that way, so you need poll() there (or something equivalent).

I would suggest simply using #ifdefs to use poll() for non-windows systems and set FD_SETSIZE to a larger value for Windows. (I did that in my workaround)

[alanxz]

I'm trying to avoid having a lot of #ifdefs if possible as it makes it more difficult to understand what is going on in the code and makes making changes to the code a more treacherous chore. Your workaround does work consistently on Win32 though.

[abogosyan]

The problem is not only FD_SETSIZE, as I described here: #168 (comment) in Linux you could stuck at recv function if nothing to receive and EINTR happened.

I'd suggest to have OS-specific functions here...