Issue #195: Actually call uselocale() in the new locale handling code in json_tokener.

Also, be sure the right locale_t is freed if we fail on the second uselocale.
Finally, fix test_locale so it *doesn't* use json_object_to_json_string as
 that will simple re-emit the original parsed string values.

tests/test_locale.expected

@@ -1,2 +1,2 @@
-new_obj.to_string()=[ 1.2, 3.4, 123456.78, 5.0, 2.3e10 ]
+new_obj.to_string()=[1.20,3.40,123456.78,5.00,23000000000.00]
 new_obj.to_string()=[1.2,3.4,123456.78,5.0,2.3e10]