Rename test_equals_none to test_cmp_none

In order to add more tests the new name is more fitting.

test/Jamfile.v2

@@ -42,7 +42,7 @@ run optional_test_inplace_factory.cpp ;
 run optional_test_io.cpp ;
 run optional_test_move.cpp ;
 run optional_test_noexcept_move.cpp ;
-run optional_test_equals_none.cpp ;
+run optional_test_cmp_none.cpp ;
 run optional_test_value_access.cpp ;
 run optional_test_emplace.cpp ;
 run optional_test_minimum_requirements.cpp ;