ENH: make sure policy is set in generated cmakelist files

Source/cmCoreTryCompile.cxx

@@ -175,6 +175,7 @@ int cmCoreTryCompile::TryCompileCode(std::vector<std::string> const& argv)
     const char* lang =(this->Makefile->GetCMakeInstance()->GetGlobalGenerator()
                         ->GetLanguageFromExtension(ext.c_str()));
     const char* def = this->Makefile->GetDefinition("CMAKE_MODULE_PATH");
+    fprintf(fout, "cmake_policy(VERSION 2.6)\n");
     if(def)
       {
       fprintf(fout, "SET(CMAKE_MODULE_PATH %s)\n", def);