Fixing read/write-u8 to block properly when srfi-18 hasn't been loaded.
Fixing read/write-u8 to block properly when srfi-18 hasn't been loaded.

norton/chibi-scheme,holmescn/chibi-scheme,norton/chibi-scheme,holmescn/chibi-scheme,norton/chibi-scheme,holmescn/chibi-scheme,norton/chibi-scheme,holmescn/chibi-scheme,norton/chibi-scheme,holmescn/chibi-scheme,norton/chibi-scheme