devmouse: add twitch mousectl command

sys/man/3/mouse

@@ -150,6 +150,10 @@ unlike
 .B reset
 clears the mouse
 to its default state.
+.TP
+.B twitch
+unblanks the screen and resets the idle timeout as if the
+mouse was twitched.
 .PD
 .PP
 Not all mice interpret all messages; with some devices,

sys/src/9/port/devmouse.c

@@ -57,6 +57,7 @@ enum
 	CMbuttonmap,
 	CMscrollswap,
 	CMswap,
+	CMtwitch,
 	CMwildcard,
 };
 
@@ -65,6 +66,7 @@ static Cmdtab mousectlmsg[] =
 	CMbuttonmap,	"buttonmap",	0,
 	CMscrollswap,	"scrollswap",	0,
 	CMswap,		"swap",		1,
+	CMtwitch,	"twitch",	0,
 	CMwildcard,	"*",		0,
 };
 
@@ -419,6 +421,10 @@ mousewrite(Chan *c, void *va, long n, vlong)
 				setbuttonmap(cb->f[1]);
 			break;
 
+		case CMtwitch:
+			drawactive(1);
+			break;
+
 		case CMwildcard:
 			mousectl(cb);
 			break;