fopen() and friends don't accept binary modes

OS-9, like Unix, makes no distinction between text and binary files; but when ANSI showed up, it specified that `fopen` needs to accept `b` even if it makes no difference, for portability with other systems that make a distinction between text and binary files. But when Kreider `fopen()` encounters `b` in a mode string, it fails with an Error 203 (Bad Mode) in `errno`.