Add BEAST_EXPECT macro:

This macro is used in the unit test framework to assist in
reporting the file and line number of test failures.

test/core/detail/empty_base_optimization.cpp

@@ -82,9 +82,9 @@ public:
     void
     run ()
     {
-        expect (test_one());
-        expect (test_two());
-        pass ();
+        BEAST_EXPECT(test_one());
+        BEAST_EXPECT(test_two());
+        pass();
     }
 };