(fraccompare, numcompare): Merge the NLS and

(fraccompare, numcompare): Merge the NLS and
non-NLS versions into a single function.

(decimal_point): Now char, since we no longer convert to unsigned char.
(th_sep): Now int, since we use a value out of char range to denote
the absence of a thousands separator.
(IS_THOUSANDS_SEP): New macro.
(USE_NEW_FRAC_COMPARE): Remove.
(nls_set_fraction): Arg is now char, not unsigned char.
Set th_sep to CHAR_MAX + 1 if there is no thousands separator.
(numcompare): Don't convert to unsigned char unless necessary.
(main): Turn off decimal points and thousand separators if they
are multibyte characters, as we don't support that yet.