Fix for multibyte characters in techo.

Works for both signed and unsigned char.

st.c

@@ -2298,7 +2298,7 @@ techo(char *buf, int len) {
 	for(; len > 0; buf++, len--) {
 		char c = *buf;
 
-		if(c < 0x20 || c == 0177) { /* control code */
+		if(BETWEEN(c, 0x00, 0x1f) || c == 0x7f) { /* control code */
 			if(c != '\n' && c != '\r' && c != '\t') {
 				c ^= '\x40';
 				tputc("^", 1);