Patch version 4 (mbcs4.patch):
 - fix encode and decode flags depending on the code page and Windows version, e.g. use WC_ERR_INVALID_CHARS instead of WC_NO_BEST_FIT_CHARS for CP_UTF8 on Windows Vista and later
 - fix usage of the default character on encoding, depending on the code page (incompatible with CP_UTF7 and CP_UTF8)
 - add some more unit tests
 - read the windows version only once, at startup
 - decode_code_page_chunk() now adjusts the input size depending on the final flag (it was done by decode_code_page_strict)