Show exit status and time in the remain-on-exit pane text, mostly from

Timo Boettcher in GitHub issue 1103.

tmux.h

@@ -778,6 +778,8 @@ struct window_pane {
 #define PANE_INPUTOFF 0x40
 #define PANE_CHANGED 0x80
 #define PANE_EXITED 0x100
+#define PANE_STATUSREADY 0x200
+#define PANE_STATUSDRAWN 0x400
 
 	int		 argc;
 	char	       **argv;