Explicit cast of 'char' to 'unsigned char' in cmd options lexer.

Explicit cast of 'char' to 'unsigned char' in cmd options lexer.

Much the same as previous commit, only this time YYCTYPE has been
erroneously set to 'char' instead of 'unsigned char. It didn't
cause any warnings or errors becase regular expressions contain
only ASCII range characters. However, relying on this is unsafe:
hypotheticlly re2c can generate some strange comparisons that compile
but fail in runtime.

Explicit cast makes sure thet all comparisons are between unsigned
values.