Setting SO_NOSIGPIPE on Socket for BSD derivatives

[pinver]

Under macOS, for example, If the socket for whatever reason is closed, you end up in the SIGPIPE handler.

Setting the SO_NOSIGPIPE option will instruct the OS to not generate SIGPIPE, but instead return EPIPE, which can be handled gracefully along with other IO errors.

[schveiguy]

I'll look into allowing this as an option.