refine an assertion message.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@28422 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/socket/test_socket.rb

@@ -290,7 +290,7 @@ class TestSocket < Test::Unit::TestCase
             msg1 = "<<<#{ai.inspect}>>>"
             s.sendmsg msg1
             unless IO.select([s], nil, nil, 10)
-              raise "no response"
+              raise "no response from #{ai.inspect}"
             end
             msg2, addr = s.recvmsg
             msg2, remote_address, local_address = Marshal.load(msg2)