sockets: support Mac OS X way of disabling SIGPIPE on a socket

Mac OS X doesn't have MSG_NOSIGNAL, so we need to use SO_NOSIGPIPE.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
TCP_client pretty much done?

Now next step is integrating it in tox.

Added TCP server functionality to bootstrap server (define TCP_RELAY_ENABLED to enable it.)