Print out the file name we're testing

We're printing out the file we're testing once we succeed, but it's hard
to know which file caused a failure. Let's add a g_test_message()
directive so we can look in our logs.

testsuite/gtk/builderparser.c

@@ -84,6 +84,7 @@ test_parse (gconstpointer d)
   GError *error = NULL;
   GString *string;
 
+  g_test_message ("filename: %s", filename);
   expected_file = get_expected_filename (filename);
 
   string = g_string_sized_new (0);