In sake of consistency with other Windows CP encodings:
* print_name is expanded to "Windows Central European (CP 1250)";
* B_MS_WINDOWS_1250_CONVERSION id looks like should be added into UTF8.h;
* mime_name set to NULL as other windows codepages have. That prevents
at least from duplicating too much 1250's in the Terminal, Mail and
StyledEdit encodings menus.