Use boost::filesystem::path::string() with std::ofstream for portability

Author: ashtum

test/beast/http/file_body.cpp

@@ -168,7 +168,7 @@ class file_body_test : public beast::unit_test::suite
             "0123456789"; // 40
         // create the temporary file
         {
-            std::ofstream fstemp(temp.path().native());
+            std::ofstream fstemp(temp.path().string());
             std::size_t written = 0;
             std::size_t to_write = 4097;
             while (written < to_write)
@@ -223,7 +223,7 @@ class file_body_test : public beast::unit_test::suite
                 "0123456789"; // 40
         // create the temporary file
         {
-            std::ofstream fstemp(temp.path().native());
+            std::ofstream fstemp(temp.path().string());
             std::size_t written = 0;
             std::size_t to_write = 2048;
             while (written < to_write)