Discard Device Control Strings and Operating System Commands.

These strings often contain things like:

- Window titles.
- Extended key map functionality.
- Color palette switching.

We could look at these features in the future (if people consider them
to be important enough), but we'd better discard them now. This fixes
some artifacts people reported when using TERM=xterm.

Reported by:	des@, Paul B. Mahol

sys/teken/sequences

@@ -88,6 +88,7 @@ ICH	Insert character			^[ [ @		n
 IL	Insert line				^[ [ L		n
 IND	Index					^[ D
 NEL	Next line				^[ E
+OSC	Operating System Command		^[ ]
 RI	Reverse index				^[ M
 RIS	Reset to Initial State			^[ c
 RM	Reset Mode				^[ [ l		r

sys/teken/teken.c

@@ -56,6 +56,7 @@ static FILE *df;
 #define	TS_WRAPPED	0x10	/* Next character should be printed on col 0. */
 #define	TS_8BIT		0x20	/* UTF-8 disabled. */
 #define	TS_CONS25	0x40	/* cons25 emulation. */
+#define	TS_INSTRING	0x80	/* Inside string. */
 
 /* Character that blanks a cell. */
 #define	BLANK	' '
@@ -176,6 +177,24 @@ static void
 teken_input_char(teken_t *t, teken_char_t c)
 {
 
+	/*
+	 * There is no support for DCS and OSC.  Just discard strings
+	 * until we receive characters that may indicate string
+	 * termination.
+	 */
+	if (t->t_stateflags & TS_INSTRING) {
+		switch (c) {
+		case '\x1B':
+			t->t_stateflags &= ~TS_INSTRING;
+			break;
+		case '\a':
+			t->t_stateflags &= ~TS_INSTRING;
+			return;
+		default:
+			return;
+		}
+	}
+
 	switch (c) {
 	case '\0':
 		break;

sys/teken/teken_subr.h

@@ -425,10 +425,11 @@ teken_subr_delete_line(teken_t *t, unsigned int nrows)
 }
 
 static void
-teken_subr_device_control_string(teken_t *t __unused)
+teken_subr_device_control_string(teken_t *t)
 {
 
-	teken_printf("device control string???\n");
+	teken_printf("Unsupported device control string\n");
+	t->t_stateflags |= TS_INSTRING;
 }
 
 static void
@@ -743,6 +744,14 @@ teken_subr_next_line(teken_t *t)
 	teken_subr_newline(t);
 }
 
+static void
+teken_subr_operating_system_command(teken_t *t)
+{
+
+	teken_printf("Unsupported operating system command\n");
+	t->t_stateflags |= TS_INSTRING;
+}
+
 static void
 teken_subr_pan_down(teken_t *t, unsigned int nrows)
 {
@@ -1258,7 +1267,10 @@ static void
 teken_subr_string_terminator(teken_t *t __unused)
 {
 
-	teken_printf("string terminator???\n");
+	/*
+	 * Strings are already terminated in teken_input_char() when ^[
+	 * is inserted.
+	 */
 }
 
 static void