Socket connection slow on Linux

[stanley90]

Hi,
I was debugging why my evals are slightly slow on a Linux server, but fast on local Mac:

Benchmark.measure { 100.times { r.eval('NULL') } }.real.to_f
=> 0.03s # on Mac
=> 4.1s # on Ubuntu (0.04s for each call)

I discovered that this can be fixed by setting this socket option in Connection#connect:

@s = TCPSocket::new(@hostname, @port_number)
@s.setsockopt(Socket::IPPROTO_TCP, Socket::TCP_NODELAY, 1)

Or in Talk#initialize, or as an optional argument to Connection (I don't know if it's safe to set globally).