Added missing includes (iostream) for the tests

test/emittertests.cpp

 #include "tests.h"
 #include "yaml-cpp/yaml.h"
+#include <iostream>
 
 namespace Test
 {

test/new-api/nodetests.cpp

 #include "nodetests.h"
 #include "yaml-cpp/yaml.h"
+#include <iostream>
 
 namespace {
 	struct TEST {

test/new-api/spectests.cpp

 #include "spectests.h"
 #include "specexamples.h"
 #include "yaml-cpp/yaml.h"
+#include <iostream>
 
 #define YAML_ASSERT(cond) do { if(!(cond)) return "  Assert failed: " #cond; } while(false)
 

test/old-api/parsertests.cpp

@@ -2,6 +2,7 @@
 #include "yaml-cpp/yaml.h"
 #include <sstream>
 #include <algorithm>
+#include <iostream>
 
 namespace Test
 {

test/spectests.cpp

 #include "spectests.h"
 #include "yaml-cpp/yaml.h"
+#include <iostream>
 
 namespace Test
 {