#14 add CP850, CP852, CP855 and KOI8-U to test_case "test_singlebyte_conv()"

References:
http://en.wikipedia.org/wiki/Code_page_850
http://en.wikipedia.org/wiki/Code_page_852
http://en.wikipedia.org/wiki/Code_page_855
http://en.wikipedia.org/wiki/KOI8-U