Avoid spawning thread for trivial getnameinfo callsHEADmaster

When calling getnameinfo we spawn a thread because it may do a slow,
blocking reverse-DNS lookup. Spawning a thread is relatively fast (~20µs
on my Linux machine) but still an order of magnitude slower than when
getnameinfo is simply translating to a numeric IP or port, which, at
least in my tests on Linux, doesn't even make a syscall.

This commit adds a fast path for when reverse DNS isn't required: either
host isn't being fetched or NI_NUMERICHOST is set AND either the
service name isn't required or NI_NUMERICSERV is set. The service name
should only need to read /etc/services, which should be fast-ish, but
is still I/O so I kept the existing behaviour (it could be on a network
fs I guess).

I tested with:

    s = TCPSocket.open("www.ruby-lang.org", 80)
    500_000.times { Socket.unpack_sockaddr_in(s.getpeername) }

Before: 12.935s
After: 0.338s

0 files changed, 0 insertions, 0 deletions