Check that TCP_NODELAY is set on upstream sockets on reconnection

Also rationalize the test to see if a function has been called.  Still
not great, but getting there :)

tests/acceptance/test_proxy_mode.rb

@@ -1,8 +1,11 @@
 require 'test/unit'
 require 'environment'
+require 'ld_preload'
 require 'proxy_tests'
 
 class TestProxyMode < Test::Unit::TestCase
+
+  include LdPreload
   include ProxyTests
 
   def setup