fix the following problem in multibyte locales.
 % echo Y | egrep -i '[y]'
 %

derived from gawk's dfa.c.

--- ./src/dfa.c.orig	2004-10-20 02:04:52.000000000 +0900
+++ ./src/dfa.c	2004-10-20 02:07:01.000000000 +0900
@@ -652,6 +652,20 @@
 	  REALLOC_IF_NECESSARY(work_mbc->chars, wchar_t, chars_al,
 			       work_mbc->nchars + 1);
 	  work_mbc->chars[work_mbc->nchars++] = (wchar_t)wc;
+	  if (case_fold && (iswlower((wint_t) wc) || iswupper((wint_t) wc)))
+	    {
+		wint_t altcase;
+
+		altcase = wc;		/* keeps compiler happy */
+		if (iswlower((wint_t) wc))
+		  altcase = towupper((wint_t) wc);
+		else if (iswupper((wint_t) wc))
+		  altcase = towlower((wint_t) wc);
+
+		REALLOC_IF_NECESSARY(work_mbc->chars, wchar_t, chars_al,
+			       work_mbc->nchars + 1);
+		work_mbc->chars[work_mbc->nchars++] = (wchar_t) altcase;
+	    }
 	}
     }
   while ((wc = wc1) != L']');