dwim_sort_func can't compare numbers against strings

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=2725

Reported by Dan Nelson dnelson_1901@yahoo.com

Array.dwim_sort_func("1", "a") fails with "Cannot compare different types." Sorry; no patch this time. 7.3's dwim_sort_func makes my head hurt compared to 7.2's implementation.