Fix ctype.h misuse.

Excluded: libtomath and libedit files, most of which appear to be
testing or example code not involved in production, and which are
derived from an upstream that should perhaps have patches submitted
upstream instead.

fix https://github.com/heimdal/heimdal/issues/1111

lib/hcrypto/test_dh.c

@@ -260,9 +260,9 @@ str2val(const char *str, int base, size_t *len)
 
     i = 0;
     for (p = str; *p != '\0'; p++) {
-	if (isxdigit((int)*p))
+	if (isxdigit((unsigned char)*p))
 	    i++;
-	else if (isspace((int)*p))
+	else if (isspace((unsigned char)*p))
 	    ;
 	else
 	    return NULL;
@@ -277,7 +277,7 @@ str2val(const char *str, int base, size_t *len)
     i = 0;
     f = 0;
     for (rp = dst, p = str; *p != '\0'; p++) {
-	if (isxdigit((int)*p)) {
+	if (isxdigit((unsigned char)*p)) {
 	    if (!f) {
 		b[0] = *p;
 		f = 1;