Cast incoming characters to unsigned char to avoid accidental sign

extension. Since ldisc_send() uses bit 8 as an internal flag, we
shouldn't be setting it except when we really want to.

[originally from svn r8989]

ldisc.c

@@ -147,7 +147,7 @@ void ldisc_send(void *handle, char *buf, int len, int interactive)
     if (EDITING) {
 	while (len--) {
 	    int c;
-	    c = *buf++ + keyflag;
+	    c = (unsigned char)(*buf++) + keyflag;
 	    if (!interactive && c == '\r')
 		c += KCTRL('@');
 	    switch (ldisc->quotenext ? ' ' : c) {