add Socket.getaddrinfo.

test/socket.rb

@@ -133,3 +133,16 @@ assert('Socket.gethostname') do
   assert_true(Socket.gethostname.is_a? String)
 end
 
+assert('Socket::getaddrinfo') do
+  ret = Socket.getaddrinfo("localhost", "domain", Socket::AF_INET, Socket::SOCK_DGRAM)
+  assert_true ret.size >= 1
+  a = ret[0]
+  assert_equal "AF_INET",           a[0]
+  assert_equal 53,                  a[1]
+  # documents says it's a hostname but CRuby returns an address
+  #assert_equal "127.0.0.1",         a[2]
+  assert_equal "127.0.0.1",         a[3]
+  assert_equal Socket::AF_INET,     a[4]
+  assert_equal Socket::SOCK_DGRAM,  a[5]
+  assert_equal Socket::IPPROTO_UDP, a[6]
+end